ScienceDaily (Dec. 28, 2011) — A UT Southwestern Medical Center study using a sophisticated "glass mouse" research model has found that multidrug-resistant tuberculosis (TB) is more likely caused in patients by speedy drug metabolism rather than inconsistent doses, as is widely believed.
If the study published in The Journal of Infectious Diseases is borne out in future investigations, it may lead to better ways to treat one of the world's major infectious diseases. Health workers worldwide currently are required to witness each administration of the combination of drugs during months of therapy.
"Tuberculosis is a common ailment, accounting for up to 3 percent of all deaths in many countries. Although effective therapy exists, there are still cases of treatment failure and drug resistance remains a threat," said Dr. Tawanda Gumbo, associate professor of internal medicine and senior author of the study.
The results seem to challenge the current approach endorsed by the World Health Organization.
Under that method, directly observed therapy-short-course strategy (DOTS), TB that responds to medication is treated with a cocktail of drugs under the supervision of health care workers, who in many countries must travel to isolated villages -- a costly and time-consuming process.
"Every TB patient is supposed to be watched as they swallow their pills in order to increase adherence and decrease emergence of drug resistance. This is the most expensive part of the program, but has been felt to be cost-effective since it improves compliance," said Dr. Gumbo, administrative director of research programs for the Office of Global Health at UT Southwestern.
In this study, UT Southwestern researchers created a sophisticated system of high-tech test tubes, which they called a "glass mouse," that mimicked standard therapy being given daily for 28 to 56 days, with dosing adherence varying between 0 percent and 100 percent. The threshold for defined non-adherence (failure to take a required dose of medication) was reached at 60 percent of the time or more.
"The first main finding in our laboratory model was that in fact non-adherence did not lead to multidrug resistance or emergence of any drug resistance in repeated studies, even when therapy failed. In fact, even when we started with a bacterial population that had been spiked with drug-resistant bacteria, non-adherence still did not lead to drug resistance," he said.
In fact, using computer simulations based on 10,000 TB patients in Cape Town, South Africa, the researchers discovered that approximately 1 percent of all TB patients with perfect adherence still developed drug resistance because they cleared the drugs from their bodies more quickly.
The body sees drugs as foreign chemicals and tries to rid itself of them, Dr. Gumbo said. A population of individuals with a genetic trait that speeds the process has been found in one area of South Africa that has a high rate of multidrug-resistant TB. In that population, patients who receive standard doses of drugs end up with concentrations in their bodies that are too low to kill the TB bacillus and drug resistance develops, he said.
A Journal of Infectious Diseases editorial that accompanies the study suggests that monitoring the levels of TB drugs in a patient's blood could be as important as monitoring compliance with therapy -- in contrast to current WHO guidelines.
"These data, based on our preclinical model, show that non-adherence alone is insufficient for the emergence of multidrug-resistant TB," Dr. Gumbo said. "It might be more cost-effective to measure patients' drug concentrations during treatment and intervene with dosage increases in those who quickly clear the drugs from their systems."
http://www.sciencedaily.com/releases/2011/12/111228111724.htm?utm_source=feedburner&utm_medium=email&utm_campaign=Feed%3A+sciencedaily+%28ScienceDaily%3A+Latest+Science+News%29
Saturday, December 31, 2011
Sunday, December 25, 2011
multiple sclerosis is not a disease of the immune system
An article to be published Friday (Dec. 23) in the December 2011 issue of The Quarterly Review of Biology argues that multiple sclerosis, long viewed as primarily an autoimmune disease, is not actually a disease of the immune system. Dr. Angelique Corthals, a forensic anthropologist and professor at the John Jay College of Criminal Justice in New York, suggests instead that MS is caused by faulty lipid metabolism, in many ways more similar to coronary atherosclerosis (hardening of the arteries) than to other autoimmune diseases.
Framing MS as a metabolic disorder helps to explain many puzzling aspects of the disease, particularly why it strikes women more than men and why cases are on the rise worldwide, Corthals says. She believes this new framework could help guide researchers toward new treatments and ultimately a cure for the disease.
Multiple sclerosis affects at least 1.3 million people worldwide. Its main characteristic is inflammation followed by scarring of tissue called myelin, which insulates nerve tissue in the brain and spinal cord. Over time, this scarring can lead to profound neurological damage. Medical researchers have theorized that a runaway immune system is at fault, but no one has been able to fully explain what triggers the onset of the disease. Genes, diet, pathogens, and vitamin D deficiency have all been linked to MS, but evidence for these risk factors is inconsistent and even contradictory, frustrating researchers in their search for effective treatment.
"Each time a genetic risk factor has shown a significant increase in MS risk in one population, it has been found to be unimportant in another," Corthals said. "Pathogens like Epstein-Barr virus have been implicated, but there's no explanation for why genetically similar populations with similar pathogen loads have drastically different rates of disease. The search for MS triggers in the context of autoimmunity simply hasn't led to any unifying conclusions about the etiology of the disease."
However, understanding MS as metabolic rather than an autoimmune begins to bring the disease and its causes into focus.
THE LIPID HYPOTHESIS
Corthals believes that the primary cause of MS can be traced to transcription factors in cell nuclei that control the uptake, breakdown, and release of lipids (fats and similar compounds) throughout the body. Disruption of these proteins, known as peroxisome proliferator-activated receptors (PPARs), causes a toxic byproduct of "bad" cholesterol called oxidized LDL to form plaques on the affected tissue. The accumulation of plaque in turn triggers an immune response, which ultimately leads to scarring. This is essentially the same mechanism involved in atherosclerosis, in which PPAR failure causes plaque accumulation, immune response, and scarring in coronary arteries.
"When lipid metabolism fails in the arteries, you get atherosclerosis," Corthals explains. "When it happens in the central nervous system, you get MS. But the underlying etiology is the same."
A major risk factor for disruption of lipid homeostasis is having high LDL cholesterol. So if PPARs are at the root of MS, it would explain why cases of the disease have been on the rise in recent decades. "In general people around the world are increasing their intake of sugars and animal fats, which often leads to high LDL cholesterol," Corthals said. "So we would expect to see higher rates of disease related to lipid metabolism—like heart disease and, in this case, MS." This also explains why statin drugs, which are used to treat high cholesterol, have shown promise as an MS treatment.
The lipid hypothesis also sheds light on the link between MS and vitamin D deficiency. Vitamin D helps to lower LDL cholesterol, so it makes sense that a lack of vitamin D increases the likelihood of the disease—especially in the context of a diet high in fats and carbohydrates.
Corthals's framework also explains why MS is more prevalent in women.
"Men and women metabolize fats differently," Corthals said. "In men, PPAR problems are more likely to occur in vascular tissue, which is why atherosclerosis is more prevalent in men. But women metabolize fat differently in relation to their reproductive role. Disruption of lipid metabolism in women is more likely to affect the production of myelin and the central nervous system. In this way, MS is to women what atherosclerosis is to men, while excluding neither sex from developing the other disease."
In addition to high cholesterol, there are several other risk factors for reduced PPAR function, including pathogens like Epstein-Barr virus, trauma that requires massive cell repair, and certain genetic profiles. In many cases, Corthals says, having just one of these risk factors isn't enough to trigger a collapse of lipid metabolism. But more than one risk factor could cause problems. For example, a genetically weakened PPAR system on its own might not cause disease, but combining that with a pathogen or with a poor diet can cause disease. This helps to explain why different MS triggers seem to be important for some people and populations but not others.
"In the context of autoimmunity, the various risk factors for MS are frustratingly incoherent," Corthals said. "But in the context of lipid metabolism, they make perfect sense."
Much more research is necessary to fully understand the role of PPARs in MS, but Corthals hopes that this new understanding of the disease could eventually lead to new treatments and prevention measures.
"This new framework makes a cure for MS closer than ever," Corthals said.
http://www.eurekalert.org/pub_releases/2011-12/uocp-rcm122211.php
Framing MS as a metabolic disorder helps to explain many puzzling aspects of the disease, particularly why it strikes women more than men and why cases are on the rise worldwide, Corthals says. She believes this new framework could help guide researchers toward new treatments and ultimately a cure for the disease.
Multiple sclerosis affects at least 1.3 million people worldwide. Its main characteristic is inflammation followed by scarring of tissue called myelin, which insulates nerve tissue in the brain and spinal cord. Over time, this scarring can lead to profound neurological damage. Medical researchers have theorized that a runaway immune system is at fault, but no one has been able to fully explain what triggers the onset of the disease. Genes, diet, pathogens, and vitamin D deficiency have all been linked to MS, but evidence for these risk factors is inconsistent and even contradictory, frustrating researchers in their search for effective treatment.
"Each time a genetic risk factor has shown a significant increase in MS risk in one population, it has been found to be unimportant in another," Corthals said. "Pathogens like Epstein-Barr virus have been implicated, but there's no explanation for why genetically similar populations with similar pathogen loads have drastically different rates of disease. The search for MS triggers in the context of autoimmunity simply hasn't led to any unifying conclusions about the etiology of the disease."
However, understanding MS as metabolic rather than an autoimmune begins to bring the disease and its causes into focus.
THE LIPID HYPOTHESIS
Corthals believes that the primary cause of MS can be traced to transcription factors in cell nuclei that control the uptake, breakdown, and release of lipids (fats and similar compounds) throughout the body. Disruption of these proteins, known as peroxisome proliferator-activated receptors (PPARs), causes a toxic byproduct of "bad" cholesterol called oxidized LDL to form plaques on the affected tissue. The accumulation of plaque in turn triggers an immune response, which ultimately leads to scarring. This is essentially the same mechanism involved in atherosclerosis, in which PPAR failure causes plaque accumulation, immune response, and scarring in coronary arteries.
"When lipid metabolism fails in the arteries, you get atherosclerosis," Corthals explains. "When it happens in the central nervous system, you get MS. But the underlying etiology is the same."
A major risk factor for disruption of lipid homeostasis is having high LDL cholesterol. So if PPARs are at the root of MS, it would explain why cases of the disease have been on the rise in recent decades. "In general people around the world are increasing their intake of sugars and animal fats, which often leads to high LDL cholesterol," Corthals said. "So we would expect to see higher rates of disease related to lipid metabolism—like heart disease and, in this case, MS." This also explains why statin drugs, which are used to treat high cholesterol, have shown promise as an MS treatment.
The lipid hypothesis also sheds light on the link between MS and vitamin D deficiency. Vitamin D helps to lower LDL cholesterol, so it makes sense that a lack of vitamin D increases the likelihood of the disease—especially in the context of a diet high in fats and carbohydrates.
Corthals's framework also explains why MS is more prevalent in women.
"Men and women metabolize fats differently," Corthals said. "In men, PPAR problems are more likely to occur in vascular tissue, which is why atherosclerosis is more prevalent in men. But women metabolize fat differently in relation to their reproductive role. Disruption of lipid metabolism in women is more likely to affect the production of myelin and the central nervous system. In this way, MS is to women what atherosclerosis is to men, while excluding neither sex from developing the other disease."
In addition to high cholesterol, there are several other risk factors for reduced PPAR function, including pathogens like Epstein-Barr virus, trauma that requires massive cell repair, and certain genetic profiles. In many cases, Corthals says, having just one of these risk factors isn't enough to trigger a collapse of lipid metabolism. But more than one risk factor could cause problems. For example, a genetically weakened PPAR system on its own might not cause disease, but combining that with a pathogen or with a poor diet can cause disease. This helps to explain why different MS triggers seem to be important for some people and populations but not others.
"In the context of autoimmunity, the various risk factors for MS are frustratingly incoherent," Corthals said. "But in the context of lipid metabolism, they make perfect sense."
Much more research is necessary to fully understand the role of PPARs in MS, but Corthals hopes that this new understanding of the disease could eventually lead to new treatments and prevention measures.
"This new framework makes a cure for MS closer than ever," Corthals said.
http://www.eurekalert.org/pub_releases/2011-12/uocp-rcm122211.php
Friday, December 23, 2011
Septin proteins take bacterial prisoners
Cellular proteins called septins might play an important part in the human body’s ability to fight off bacterial infections, according to a study.
Septins are found in many organisms, and are best known for building scaffolding to provide structural support during cell division and to rope off parts of the cell. However, most studies of septins, or guanosine-5′-triphosphate (GTP) binding proteins, have been confined to yeast cells. The latest research in human cells suggests that septins build 'cages' around bacterial pathogens, immobilizing the harmful microbes and preventing them from invading other healthy cells.
Septin proteins build cages (red) to trap bacteria (blue) that invade human cells.
S. Mostowy
This cellular defence system could help researchers to create therapies for dysentery and other illnesses, the researchers say. “This is a new way for cells to control an infection,” says Pascale Cossart, a cell biologist at the Pasteur Institute in Paris, who presented the findings in a poster session on Sunday at the annual meeting of the American Society for Cell Biology in Denver, Colorado.
The researchers discovered the caging behaviour with Shigella, a bacterium that causes sometimes lethal diarrhoea in humans and other primates. To propagate from cell to cell, Shigella bacteria develop actin-polymer 'tails', which propel the microbes around and allow them to force their way into neighbouring host cells. To counterattack, human cells produce a cell-signalling protein called TNF-α. The researchers found that when TNF-α is present, thick bundles of septin filaments encircle the microbes. This, in turn, interferes with tail formation and stops Shigella in its tracks1, 2.
Microbes that become trapped in septin cages are broken down in a stage of the cell's life cycle called autophagy. “Autophagy is more efficient because of the septin cage, and the septin cage does not occur if you do not have the autophagy,” says Cossart.
Joining the dots
The work “implies that septins are more dynamic than originally thought”, says Alexis Gautreau, a cell biologist at the French National Research Agency in Gif-sur-Yvette. Until now, he says, the function of septins in helping yeast cells to divide was well known, “but no one could relate that to mammalian cell physiology”.
“Septin’s role is pretty mysterious,” agrees Harry Higgs, a biochemist at Dartmouth Medical School in Hanover, New Hampshire. “The cool thing to me is that pathogenic bacteria have been so instrumental in figuring out how actin works, and this is the first sign that they will help to figure out how septins work.”
The researchers are now working to better understand the link between septins and autophagy, and to determine how important septins are in humans in vivo.
Previous studies have suggested that disruptions in septins and mutations in the genes that code for them could be involved in causing leukaemia, colon cancer and neurodegenerative conditions such as Parkinson’s disease and Alzheimer’s disease. Potential therapies for these, as well as for bacterial conditions such as dysentery caused by Shigella, might bolster the body’s immune system with drugs that mimic the behaviour of TNF-α and allow the septin cages to proliferate, says Cossart. “If you have a way to increase the number of cages, you have a new way to fight against infection,” she adds.
http://www.nature.com/news/septin-proteins-take-bacterial-prisoners-1.9540?WT.ec_id=NEWS-20111206
Septins are found in many organisms, and are best known for building scaffolding to provide structural support during cell division and to rope off parts of the cell. However, most studies of septins, or guanosine-5′-triphosphate (GTP) binding proteins, have been confined to yeast cells. The latest research in human cells suggests that septins build 'cages' around bacterial pathogens, immobilizing the harmful microbes and preventing them from invading other healthy cells.
Septin proteins build cages (red) to trap bacteria (blue) that invade human cells.
S. Mostowy
This cellular defence system could help researchers to create therapies for dysentery and other illnesses, the researchers say. “This is a new way for cells to control an infection,” says Pascale Cossart, a cell biologist at the Pasteur Institute in Paris, who presented the findings in a poster session on Sunday at the annual meeting of the American Society for Cell Biology in Denver, Colorado.
The researchers discovered the caging behaviour with Shigella, a bacterium that causes sometimes lethal diarrhoea in humans and other primates. To propagate from cell to cell, Shigella bacteria develop actin-polymer 'tails', which propel the microbes around and allow them to force their way into neighbouring host cells. To counterattack, human cells produce a cell-signalling protein called TNF-α. The researchers found that when TNF-α is present, thick bundles of septin filaments encircle the microbes. This, in turn, interferes with tail formation and stops Shigella in its tracks1, 2.
Microbes that become trapped in septin cages are broken down in a stage of the cell's life cycle called autophagy. “Autophagy is more efficient because of the septin cage, and the septin cage does not occur if you do not have the autophagy,” says Cossart.
Joining the dots
The work “implies that septins are more dynamic than originally thought”, says Alexis Gautreau, a cell biologist at the French National Research Agency in Gif-sur-Yvette. Until now, he says, the function of septins in helping yeast cells to divide was well known, “but no one could relate that to mammalian cell physiology”.
“Septin’s role is pretty mysterious,” agrees Harry Higgs, a biochemist at Dartmouth Medical School in Hanover, New Hampshire. “The cool thing to me is that pathogenic bacteria have been so instrumental in figuring out how actin works, and this is the first sign that they will help to figure out how septins work.”
The researchers are now working to better understand the link between septins and autophagy, and to determine how important septins are in humans in vivo.
Previous studies have suggested that disruptions in septins and mutations in the genes that code for them could be involved in causing leukaemia, colon cancer and neurodegenerative conditions such as Parkinson’s disease and Alzheimer’s disease. Potential therapies for these, as well as for bacterial conditions such as dysentery caused by Shigella, might bolster the body’s immune system with drugs that mimic the behaviour of TNF-α and allow the septin cages to proliferate, says Cossart. “If you have a way to increase the number of cages, you have a new way to fight against infection,” she adds.
http://www.nature.com/news/septin-proteins-take-bacterial-prisoners-1.9540?WT.ec_id=NEWS-20111206
Saturday, December 17, 2011
Why Tuberculosis Is So Hard to Cure
When microbes divide, you usually get more of the same: A cell splits up and creates two identical copies of itself. But a new study shows that's not true for mycobacteria, which cause tuberculosis (TB) in humans—and that may explain why the disease is so difficult to treat. Mycobacteria divide asymmetrically, generating a population of cells that grow at different rates, have different sizes, and differ in how susceptible they are to antibiotics, increasing the chances that at least some will survive. Researchers hope the findings will help them develop drugs against those cells that are especially hard to kill.
"It is incredible that we are finding such basic things out only now," says immunologist Sarah Fortune of at the Harvard School of Public Health in Boston, the paper's lead author. "But it reflects the fact that mycobacteria are relatively understudied."
More than a third of the world's population is estimated to be infected with Mycobacterium tuberculosis. Most people's immune system can keep the bacteria in check, but there is a lifetime chance of 1 in 10 that the dormant infection will progress to TB; the disease still kills 4000 people every day. Tuberculosis treatment is a combination of antibiotics taken for half a year or more—a major drawback, because patients often quit therapy prematurely, increasing the risk of drug-resistant strains emerging. Scientists have assumed that mycobacteria are so hard to kill because dormant cells exist even in patients with active disease and these cells are far less susceptible to antibiotics than metabolically active bacteria.
But Fortune and her colleagues found a second, more surprising mechanism. They cultured M. smegmatis, which is closely related to M. tuberculosis but faster growing, in a tiny chamber with a constant flow of nutrients, allowing them to watch single live cells growing and replicating. Unlike other rod-shaped bacteria, such as E. coli, mycobacterial cells divided asymmetrically, creating a tapestry of cell types with widely different sizes and growth rates, the team reports online today in Science.
By labeling the cell wall of the mycobacteria with a fluorescent dye and observing the new, unstained cell wall growing at the poles, the researchers found that daughter cells mainly grow at their "old" pole. As the new end, created by the cell division, grows older, it matures and the cell elongates faster. And as the cells go through numerous divisions, cells with poles of many different "ages" emerge, leading to the wide variety in growth rates.
Importantly, the cells also differed in their susceptibility to antibiotics: While "older," fast-growing cells were more susceptible to the drugs isoniazid and cycloserine; younger, slower-growing cells were more susceptible to rifampicin. "When I started working on mycobacteria, the assumption was that all the bacteria are indistinguishable. This is the first mechanistic insight into why the cells are phenotypically different," says Fortune. The asymmetry is a way for mycobacteria to keep their population diverse, she says, just like viruses create diversity by mutating frenetically.
"This is an important study, because it shows that our way of thinking that populations are the sum of equal organisms is incorrect," says immunologist Stefan Kaufmann of the Max Planck Institute for Infection Biology in Berlin. "As we look at individual microbes, we find diversity." Kaufmann cautions, however, that most of the experiments were done with M. smegmatis and need to be verified with M. tuberculosis. "But this could explain, at least in part, why tuberculosis is so hard to treat," he says. "And it could pave the way for a rational search for new combination therapies composed of drugs that attack the different types of bacteria."
http://news.sciencemag.org/sciencenow/2011/12/why-tuberculosis-is-so-hard-to.html?ref=em&elq=d661ccc382b64524836cc194d7243fc5
"It is incredible that we are finding such basic things out only now," says immunologist Sarah Fortune of at the Harvard School of Public Health in Boston, the paper's lead author. "But it reflects the fact that mycobacteria are relatively understudied."
More than a third of the world's population is estimated to be infected with Mycobacterium tuberculosis. Most people's immune system can keep the bacteria in check, but there is a lifetime chance of 1 in 10 that the dormant infection will progress to TB; the disease still kills 4000 people every day. Tuberculosis treatment is a combination of antibiotics taken for half a year or more—a major drawback, because patients often quit therapy prematurely, increasing the risk of drug-resistant strains emerging. Scientists have assumed that mycobacteria are so hard to kill because dormant cells exist even in patients with active disease and these cells are far less susceptible to antibiotics than metabolically active bacteria.
But Fortune and her colleagues found a second, more surprising mechanism. They cultured M. smegmatis, which is closely related to M. tuberculosis but faster growing, in a tiny chamber with a constant flow of nutrients, allowing them to watch single live cells growing and replicating. Unlike other rod-shaped bacteria, such as E. coli, mycobacterial cells divided asymmetrically, creating a tapestry of cell types with widely different sizes and growth rates, the team reports online today in Science.
By labeling the cell wall of the mycobacteria with a fluorescent dye and observing the new, unstained cell wall growing at the poles, the researchers found that daughter cells mainly grow at their "old" pole. As the new end, created by the cell division, grows older, it matures and the cell elongates faster. And as the cells go through numerous divisions, cells with poles of many different "ages" emerge, leading to the wide variety in growth rates.
Importantly, the cells also differed in their susceptibility to antibiotics: While "older," fast-growing cells were more susceptible to the drugs isoniazid and cycloserine; younger, slower-growing cells were more susceptible to rifampicin. "When I started working on mycobacteria, the assumption was that all the bacteria are indistinguishable. This is the first mechanistic insight into why the cells are phenotypically different," says Fortune. The asymmetry is a way for mycobacteria to keep their population diverse, she says, just like viruses create diversity by mutating frenetically.
"This is an important study, because it shows that our way of thinking that populations are the sum of equal organisms is incorrect," says immunologist Stefan Kaufmann of the Max Planck Institute for Infection Biology in Berlin. "As we look at individual microbes, we find diversity." Kaufmann cautions, however, that most of the experiments were done with M. smegmatis and need to be verified with M. tuberculosis. "But this could explain, at least in part, why tuberculosis is so hard to treat," he says. "And it could pave the way for a rational search for new combination therapies composed of drugs that attack the different types of bacteria."
http://news.sciencemag.org/sciencenow/2011/12/why-tuberculosis-is-so-hard-to.html?ref=em&elq=d661ccc382b64524836cc194d7243fc5
Friday, December 16, 2011
Red-type Rubiscos
Structural analyses of the first identified activase for red-type Rubiscos reveal key insights into Rubisco activation.
The authors propose that Cbbx (left) releases RuBP from Rubisco (right) through transient interactions with the C-terminal tail of the Rubisco large subunit (red wire). Figure courtesy of Andreas Bracher.
Red-type Rubiscos, present in photosynthetic bacteria, red algae, and phytoplankton, are responsible for most of the oceanic carbon uptake. Understanding the catalytic cycle of red-type Rubiscos could therefore aid in improving the CO2 uptake and biomass productions of photosynthetic organisms.
Rubiscos catalyze the carboxylation of Ribulose-1,5-bisphosphate (RuBP) by CO2 in the first step of carbon fixation in photosynthesis. Binding of Rubisco to RuBP in the absence of active site carbamylation creates an inactive complex that must be reactivated by Rubisco activase (Rca), which catalyzes the release of RuBP from Rubisco in an ATP-dependent manner. While Rca has been identified in green algae and plants, no Rca homolog has been identified in organisms containing red-type Rubiscos.
Mueller-Cajar and colleagues have now identified and characterized the Rubisco activase CbbX from the proteobacterium Rhodobacter sphaeroides. Like Rca, CbbX is an AAA+ protein with ATPase activity and is able to activate inhibited Rubisco in the presence of ATP. Unlike Rca, CbbX has no inherent ATPase activity in the absence of RuBP. Therefore, RuBP acts as an allosteric regulator of CbbX and ensures that the enzyme is only active during photosynthesis, when levels of RuBP are high.
Analysis of CbbX by negative stain electron microscopy revealed that CbbX forms ring-like structures similar to other AAA+ proteins in the presence of ATP and RuBP. The crystal structure of CbbX reveals a typical AAA+ fold with an N-terminal α/β domain and a C-terminal α-helical domain. The α/β domain contains the canonical Walker A and B motifs, which are important for binding ATP, and a conserved pore loop. The position of two bound sulfate ions in the α-helical domain reveals the likely binding site for RuBP.
Based on structural analyses, the authors proposed a model for Rubisco activation in which the C-terminal extension present in red-type Rubiscos, but not green-type Rubiscos, is pulled into the core of CbbX by the conserved pore loop. This pulling force opens up the active site of Rubisco and enables the inhibitory RuBP molecule to leave.
Jennifer Cable
References:
O. Mueller-Cajar et al. Structure and function of the AAA+ protein CbbX, a red-type Rubisco activase.
Nature. 479, 194-199 (2011). doi:10.1038/nature10568
The authors propose that Cbbx (left) releases RuBP from Rubisco (right) through transient interactions with the C-terminal tail of the Rubisco large subunit (red wire). Figure courtesy of Andreas Bracher.
Red-type Rubiscos, present in photosynthetic bacteria, red algae, and phytoplankton, are responsible for most of the oceanic carbon uptake. Understanding the catalytic cycle of red-type Rubiscos could therefore aid in improving the CO2 uptake and biomass productions of photosynthetic organisms.
Rubiscos catalyze the carboxylation of Ribulose-1,5-bisphosphate (RuBP) by CO2 in the first step of carbon fixation in photosynthesis. Binding of Rubisco to RuBP in the absence of active site carbamylation creates an inactive complex that must be reactivated by Rubisco activase (Rca), which catalyzes the release of RuBP from Rubisco in an ATP-dependent manner. While Rca has been identified in green algae and plants, no Rca homolog has been identified in organisms containing red-type Rubiscos.
Mueller-Cajar and colleagues have now identified and characterized the Rubisco activase CbbX from the proteobacterium Rhodobacter sphaeroides. Like Rca, CbbX is an AAA+ protein with ATPase activity and is able to activate inhibited Rubisco in the presence of ATP. Unlike Rca, CbbX has no inherent ATPase activity in the absence of RuBP. Therefore, RuBP acts as an allosteric regulator of CbbX and ensures that the enzyme is only active during photosynthesis, when levels of RuBP are high.
Analysis of CbbX by negative stain electron microscopy revealed that CbbX forms ring-like structures similar to other AAA+ proteins in the presence of ATP and RuBP. The crystal structure of CbbX reveals a typical AAA+ fold with an N-terminal α/β domain and a C-terminal α-helical domain. The α/β domain contains the canonical Walker A and B motifs, which are important for binding ATP, and a conserved pore loop. The position of two bound sulfate ions in the α-helical domain reveals the likely binding site for RuBP.
Based on structural analyses, the authors proposed a model for Rubisco activation in which the C-terminal extension present in red-type Rubiscos, but not green-type Rubiscos, is pulled into the core of CbbX by the conserved pore loop. This pulling force opens up the active site of Rubisco and enables the inhibitory RuBP molecule to leave.
Jennifer Cable
References:
O. Mueller-Cajar et al. Structure and function of the AAA+ protein CbbX, a red-type Rubisco activase.
Nature. 479, 194-199 (2011). doi:10.1038/nature10568
Saturday, December 10, 2011
Children with HIV in Asia Suffer Resistance to AIDS Drugs
Researchers with the HIV/AIDS network TREAT Asia are calling for improved access to advanced pediatric HIV drugs. The collaboration of clinics, hospitals, and research institutions has released a new long-term study of 4,000 patients under age 23 in six Asian countries: It finds growing evidence of drug resistance and loss of bone density among the youths.
“In our cohort, about 14 percent of the children have failed first-line drugs ... . Some of the children who are already on second-line [drugs] are under the age of five,” said TREAT Asia Director Annette Sohn, a pediatric HIV/AIDS specialist.
Drug resistance can be caused by poor adherence to AIDS drug regimens, though in Asia it also is due to a lack of formulations for children. “We all made some mistakes on how we managed patients with HIV in the beginning of the epidemic,” said Sohn. “We used adult tablets, we had no pediatric formulations in our countries.”
“Unless we develop access to third-line drugs, we are going to find ourselves in a clinic room with a patient that there is nothing left and we have no other drug to give them,” Sohn said.
The study - carried out in Cambodia, India, Indonesia, Malaysia, Thailand, and Vietnam - found a high percentage of teenage patients with low bone mineral density, a precursor to osteoporosis. “We did a special X-ray on these teenagers, who are about 16 years old, and found that 15 percent of them had low bone mass,” Sohn said. “This is not normal. Kids are not supposed to have low bone mass when they’re 16 years old and that’s because of the effect of HIV on their bodies ... brain, bone, immune system.”
Though she noted this may also be due to toxic effects that some AIDS drugs, such tenofovir, have on bone, Sohn added, “It is not so much about avoiding one drug or another but being aware of these side effects, studying what drug doses will suppress the virus while not being toxic, having the resources to monitor side effects, and having access to alternative drugs if they do arise.”
Reuters (12.01.11):: Tan Ee Lyn
“In our cohort, about 14 percent of the children have failed first-line drugs ... . Some of the children who are already on second-line [drugs] are under the age of five,” said TREAT Asia Director Annette Sohn, a pediatric HIV/AIDS specialist.
Drug resistance can be caused by poor adherence to AIDS drug regimens, though in Asia it also is due to a lack of formulations for children. “We all made some mistakes on how we managed patients with HIV in the beginning of the epidemic,” said Sohn. “We used adult tablets, we had no pediatric formulations in our countries.”
“Unless we develop access to third-line drugs, we are going to find ourselves in a clinic room with a patient that there is nothing left and we have no other drug to give them,” Sohn said.
The study - carried out in Cambodia, India, Indonesia, Malaysia, Thailand, and Vietnam - found a high percentage of teenage patients with low bone mineral density, a precursor to osteoporosis. “We did a special X-ray on these teenagers, who are about 16 years old, and found that 15 percent of them had low bone mass,” Sohn said. “This is not normal. Kids are not supposed to have low bone mass when they’re 16 years old and that’s because of the effect of HIV on their bodies ... brain, bone, immune system.”
Though she noted this may also be due to toxic effects that some AIDS drugs, such tenofovir, have on bone, Sohn added, “It is not so much about avoiding one drug or another but being aware of these side effects, studying what drug doses will suppress the virus while not being toxic, having the resources to monitor side effects, and having access to alternative drugs if they do arise.”
Reuters (12.01.11):: Tan Ee Lyn
Saturday, December 3, 2011
Simple blood test diagnoses Parkinson's disease long before symptoms appear
New research in the FASEB Journal suggests that phosphorylated alpha-synuclein, a substance found in the blood of Parkinson's patients, could lead to definitive diagnostic tool
Bethesda, MD—A new research report appearing in the December issue of the FASEB Journal (http://www.fasebj.org) shows how scientists from the United Kingdom have developed a simple blood test to detect Parkinson's disease even at the earliest stages. The test is possible because scientists found a substance in the blood, called "phosphorylated alpha-synuclein," which is common in people with Parkinson's disease, and then developed a way to identify its presence in our blood.
"A blood test for Parkinson's disease would mean you could find out if a person was in danger of getting the disease, before the symptoms started," said David Allsop, Ph.D., a researcher involved in the work from the Division of Biomedical and Life Sciences and the School of Health and Medicine at the University of Lancaster, in Lancaster, UK. "This would help the development of medicines that could protect the brain, which would be better for the quality of life and future health of older people."
To develop the blood test for Parkinson's disease, Allsop and colleagues studied a group of people diagnosed with the disease and a second group of healthy people of a similar age. Blood samples from each group were analyzed to determine the levels of phosphorylated alpha-synuclein present. They found those with Parkinson's disease had increased levels of the substance. Based upon these findings, researchers developed a blood test that detects the presence of phosphorylated alpha-synuclein, which could allow for diagnosis of the disease well before symptoms appear but when brain damage has already begun to occur.
"When most people think of Parkinson's disease, they think of the outward symptoms, such as involuntary movements," said Gerald Weissmann, M.D., Editor-in-Chief of the FASEB Journal, "but many people with Parkinson's also develop neurological problems that may be more difficult to detect right away. Having a blood test not only helps doctors rule out other possible causes of the outward symptoms, but it also allows for early detection which can help patients and their caregivers prepare for the possibility of the mental, emotional, and behavioral problems that the disease can cause."
http://www.eurekalert.org/pub_releases/2011-11/foas-sbt113011.php
Bethesda, MD—A new research report appearing in the December issue of the FASEB Journal (http://www.fasebj.org) shows how scientists from the United Kingdom have developed a simple blood test to detect Parkinson's disease even at the earliest stages. The test is possible because scientists found a substance in the blood, called "phosphorylated alpha-synuclein," which is common in people with Parkinson's disease, and then developed a way to identify its presence in our blood.
"A blood test for Parkinson's disease would mean you could find out if a person was in danger of getting the disease, before the symptoms started," said David Allsop, Ph.D., a researcher involved in the work from the Division of Biomedical and Life Sciences and the School of Health and Medicine at the University of Lancaster, in Lancaster, UK. "This would help the development of medicines that could protect the brain, which would be better for the quality of life and future health of older people."
To develop the blood test for Parkinson's disease, Allsop and colleagues studied a group of people diagnosed with the disease and a second group of healthy people of a similar age. Blood samples from each group were analyzed to determine the levels of phosphorylated alpha-synuclein present. They found those with Parkinson's disease had increased levels of the substance. Based upon these findings, researchers developed a blood test that detects the presence of phosphorylated alpha-synuclein, which could allow for diagnosis of the disease well before symptoms appear but when brain damage has already begun to occur.
"When most people think of Parkinson's disease, they think of the outward symptoms, such as involuntary movements," said Gerald Weissmann, M.D., Editor-in-Chief of the FASEB Journal, "but many people with Parkinson's also develop neurological problems that may be more difficult to detect right away. Having a blood test not only helps doctors rule out other possible causes of the outward symptoms, but it also allows for early detection which can help patients and their caregivers prepare for the possibility of the mental, emotional, and behavioral problems that the disease can cause."
http://www.eurekalert.org/pub_releases/2011-11/foas-sbt113011.php
Medical researchers in Canada and the US discover hidden side of prion diseases
Medical researchers in Canada and the United States recently published their joint findings that fatal prion diseases, which include BSE or "mad cow disease," have a hidden signature.
Findings published this month in the peer-reviewed journal, Public Library of Science (PLoS) Pathogens, demonstrate that up to seven months before an animal shows physical signs of having a prion infection, a particular prion protein in the brain was being eradicated. This member of the prion family is known as shadoo protein.
"What we discovered is that as the early prion disease process unfolds in an infected brain, that the shadoo protein is simultaneously disappearing," said lead author and co-principal investigator, David Westaway, a researcher in the Faculty of Medicine & Dentistry at the University of Alberta.
"This is telling us there is a process within the disease that we were previously unaware of, a process that is happening before the infected animals are getting sick. It's telling us that the brain cells are more active in defending themselves than what we thought they were. The brain cells are in fact trying to get rid of the prion protein and as a consequence, this bystander shadoo protein is being destroyed unintentionally.
"This finding suggests that prion diseases are dynamic and not necessarily unstoppable, that there could be a cellular process trying to destroy the infectious prions as they appear. And if we could help that process a little bit more, that might be an avenue to attenuate the disease."
Westaway, who works in both the Division of Neurology of the Faculty of Medicine & Dentistry, and the Centre for Prions and Protein Folding Diseases at the U of A, collaborated with a team of researchers from Ontario, the University of California, the Institute for Systems Biology in Washington, the McLaughlin Research Institute in Montana and a researcher in Germany, on this discovery.
The same day this paper was published, very similar findings were published by a team of researchers from the University of California, which demonstrates "these new chemical changes are a concrete and reproducible hallmark of prion disease," says Westaway.
Co-principal investigator George Carlson, from the McLaughlin Research Institute, added: "Given that shadoo may be destroyed by a process that actually targets infectious prions, it was surprising that when we increased the amount of shadoo in laboratory models that the course of disease was not changed. We need to understand why."
The next step for Westaway's research team is to determine why this shadoo protein is disappearing.
The finding opens up a new window of research opportunities.
"We need to better understand this. We want to solve this mystery," he says.
http://www.eurekalert.org/pub_releases/2011-11/uoaf-mri112811.php
Findings published this month in the peer-reviewed journal, Public Library of Science (PLoS) Pathogens, demonstrate that up to seven months before an animal shows physical signs of having a prion infection, a particular prion protein in the brain was being eradicated. This member of the prion family is known as shadoo protein.
"What we discovered is that as the early prion disease process unfolds in an infected brain, that the shadoo protein is simultaneously disappearing," said lead author and co-principal investigator, David Westaway, a researcher in the Faculty of Medicine & Dentistry at the University of Alberta.
"This is telling us there is a process within the disease that we were previously unaware of, a process that is happening before the infected animals are getting sick. It's telling us that the brain cells are more active in defending themselves than what we thought they were. The brain cells are in fact trying to get rid of the prion protein and as a consequence, this bystander shadoo protein is being destroyed unintentionally.
"This finding suggests that prion diseases are dynamic and not necessarily unstoppable, that there could be a cellular process trying to destroy the infectious prions as they appear. And if we could help that process a little bit more, that might be an avenue to attenuate the disease."
Westaway, who works in both the Division of Neurology of the Faculty of Medicine & Dentistry, and the Centre for Prions and Protein Folding Diseases at the U of A, collaborated with a team of researchers from Ontario, the University of California, the Institute for Systems Biology in Washington, the McLaughlin Research Institute in Montana and a researcher in Germany, on this discovery.
The same day this paper was published, very similar findings were published by a team of researchers from the University of California, which demonstrates "these new chemical changes are a concrete and reproducible hallmark of prion disease," says Westaway.
Co-principal investigator George Carlson, from the McLaughlin Research Institute, added: "Given that shadoo may be destroyed by a process that actually targets infectious prions, it was surprising that when we increased the amount of shadoo in laboratory models that the course of disease was not changed. We need to understand why."
The next step for Westaway's research team is to determine why this shadoo protein is disappearing.
The finding opens up a new window of research opportunities.
"We need to better understand this. We want to solve this mystery," he says.
http://www.eurekalert.org/pub_releases/2011-11/uoaf-mri112811.php
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