Beyond crystals, solutions and powders

A new approach improves the functionality of an alternative use for synchrotron beams.

Synchrotron beams, the long- and much-appreciated workhorse of structural biologists for X-ray crystallography, small-angle X-ray scattering (SAXS) and other techniques, are perfect for these applications because of their high intensity, high polarization and low angular divergence. However, the stable and bright nature of their radiation also makes them excellent energy sources for other applications, including Fourier transform infrared (FTIR) imaging—a technique that generates images based on the infrared spectrum of biological samples.
FTIR imaging has an advantage over traditional microscopy as it does not require chemical labeling of samples with dyes, stains or tagged biomolecules. Instead, it uses mid-infrared absorption to produce an image by focal plane array (FPA) detection, with no additional processing of the sample needed. The image is determined by how areas of the sample respond to specific infrared wavelengths.
One challenge of FTIR microspectroscopy has been the lack of brightness and spatial resolution available from thermal sources of mid-infrared radiation, the traditional energy sources used in this technique. Previous work addressed this problem by adapting FTIR microspectroscopy to work with a synchrotron beam coupled to a mercury-cadmium-telluride detector (for raster scanning measurements), which led to significant improvements in the signal-to-noise ratio. The downside of the synchrotron approach was the low angular divergence of the synchrotron beam, which necessarily illuminates a small area and led to exceedingly long data collection times. Now, Hirschmugl and colleagues have addressed this issue and improved the utility of FTIR microspectroscopy.
Using a specially designed system, the authors split a fan of synchrotron beam radiation into 12 individual beams that were then bundled to illuminate a larger field of view before being collected by an FPA detector. The end result was a near 100-fold improvement in pixel size relative to thermal radiation sources, which allowed them to identify specific components of tissue samples. Without any additional chemical labeling, the authors were able to distinguish cell types, epithelial and stromal areas in tumor samples, and even high-collagen areas on the basis of their different absorption spectra.
One of the most pronounced benefits of the bundled beam approach was the time necessary for image acquisition. A 280 × 310 μm area required only 30 min for acquisition at diffraction-limited resolution, whereas the previous system using a synchrotron beam source would have required 11 d. The combination of high spatial resolution with substantially improved image acquisition time will undoubtedly make FTIR imaging using a synchrotron multi-beam source a vital technique for researchers looking for detailed images with minimal processing of their samples.

Steve Mason

A2A Adenosine Receptor

SBKB [doi:10.3942/psi_sbkb/fm_2011_05]
With proteins, small motions often have large effects. A new structure of the A_2A adenosine receptor reveals these motions for an important class of proteins: the G protein-coupled receptors. GPCRs transmit messages across cell membranes, capturing signaling molecules like adrenaline and dopamine, shifting shape, and launching a cascade of messages inside the cell. The atomic details of this signaling has been largely a mystery, since previous structures show the receptor in an inactive state. The new structure fills out the story, and captures the receptor in the activated state, after it has bound to its signaling ligand.

Signaling with Nucleosides

Adenosine receptors are found on cells throughout the body, where they play many different roles. There are four different kinds, each with a different spectrum of responses when activated, controlling diverse processes such as pain, blood flow, respiration, and sleep. Often, the different receptors can have opposite effects. For instance, some forms enhance inflammation when they bind to adenosine, but the A_2A adenosine receptor reduces inflammation. This makes them quite challenging as targets for drug action, since it is important to block only the desired receptor, and not the others.

Inflammatory Responses

The A_2A adenosine receptor plays an important role in controlling inflammatory responses, and thus is a target for development of anti-inflammatory drugs. For instance, a drug that binds to this receptor and activates it could be useful for the treatment of asthma and COPD (chronic obstructive pulmonary disease), two diseases where the lungs become inflamed, limiting the amount of air reaching the body. This type of drug is termed an "agonist", as opposed to "antagonists" that block the action of the target protein. Researchers have been searching for both types of drugs: agonists to activate the A_2A receptor, and antagonists to block other receptors that increase inflammation.

Shifting Shapes

The new structure, solved by Ray Stevens and coworkers at PSI, captures the A_2A adenosine receptor bound to an effective agonist drug (PDB entry 3qak). The receptor adopts a slightly different shape than that seen in a previous structure with an antagonist drug (PDB entry 3eml). The receptor is composed of seven helices stacked side-by-side, and these helices slide relative to one another when the drug binds. The ribose portion of the drug seems to be the key player in this motion. Both the agonist and antagonist have a similar adenine ring, but only the agonist has a typical nucleoside sugar. It interacts with the helices surrounding the binding site, shifting them by several Angstroms. This motion is propagated inside, where it is presumably sensed by G-proteins, leading to the signaling cascade. To take a closer look at this motion, click on the image for an interactive Jmol.

NEW TB TEST TO DETECT MORE PEOPLE WHO NEED DR-TB TREATMENT

MSF report says fixing drug supply and price problems is urgent

Geneva/Johannesburg, 23 March 2011 – A promising new diagnostic test will
finally help detect more people with drug-resistant tuberculosis (DR-TB),
increasing the urgency to solve major problems around the pricing and
supply of DR-TB medicines, according to a new report by the international
medical humanitarian organisation Médecins Sans Frontières (MSF). DR-TB is
on the rise, but less than 7% of 440,000 new cases each year receive
treatment, and DR-TB kills 150,000 people annually WHO.
The treatment of DR-TB relies on old antibiotics, many of which have severe
side effects, ranging from constant nausea to deafness, and must be taken
as complex regimens – patients must take up to 17 pills every day for up to
two years. However, these are the only drugs that exist today that can
tackle DR-TB.  MSF’s report shows that these drugs are riddled with
persistent supply and price problems that must be urgently addressed.
“Patients have been stuck in a vicious circle – not enough people are
diagnosed, and drug supply problems along with high prices stand in the way
of putting more people on treatment,” said Dr. Tido von Schoen-Angerer,
Executive Director of MSF’s Campaign for Access to Essential Medicines.
“The low demand for DR-TB drugs has made the market unattractive for
producers, which is reinforcing supply and price problems.”
MSF’s report examined medicines used to treat DR-TB according to the number
of suppliers, quality assurance and price, based on information obtained
from the Global Drug Facility and drug manufacturers.  It found that four
of the recommended medicines are available from only one quality-assured
source. Relying on a sole supplier whose production could be disrupted or
stopped at any time always carries a risk of dangerous treatment
interruption for patients. For example, supplies of the injectable drug
kanamycin were disrupted during 2010, leading to a temporary global
stockout.
Additionally, MSF’s report found that several DR-TB medicines are very
expensive, with prices for two drugs having increased by more than 600% and
one drug by more than 800% over the last decade.  A 24-month DR-TB
treatment regimen can cost as much as US$9,000 for one patient – 470 times
more than the $19 per patient it costs to cure standard, drug-sensitive TB.
“Now that we have a new test that can detect DR-TB in less than two hours
instead of three months, we’re going to see many more people who will need
reliable drug supplies to get cured,” said Dr. Jennifer Hughes of MSF in
Khayelitsha, South Africa. MSF is rolling out the new test in 15 countries
this year. “We need to see some immediate action to resolve these problems
and improve access to DR-TB drugs so that more people are started on
treatment and transmission of this disease is reduced,” said Dr. Hughes.
One way to kickstart increased production of some of these drugs is for
donors to guarantee purchase volumes for several years to producers
upfront. Other mechanisms such as better forecasting of the mid- to
long-term needs for DR-TB drugs are also needed to help attract more
producers to the market, to improve supply security and increase
competition that helps brings prices down.
 “We have developed a model of managing DR-TB within the community that can
be scaled up to allow increased access to treatment in high HIV prevalent
settings. With faster diagnosis and better treatment models of DR-TB we
need to fix the supply and price issues with DR-TB drugs. We also need to
see new drugs developed,” said Dr. Hughes.
Joanna Keenan
Press Officer
Campaign for Access to Essential Medicines
Medecins Sans Frontieres
joanna.keenan [at] geneva.msf.org