Protein study gives fresh impetus in fight against superbugs

Researchers have mapped the complex molecular structure of an enzyme found in many bacteria. These molecules – known as restriction enzymes – control the speed at which bacteria can acquire resistance to drugs and eventually become superbugs.

The study, carried out by an international team including scientists from the University of Edinburgh, focused on E. coli, but the results would apply to many other infectious bacteria.

After prolonged treatment with antibiotics, bacteria may evolve to become resistant to many drugs, as is the case with superbugs such as MRSA.

Bacteria become resistant by absorbing DNA – usually from other bugs or viruses – which contains genetic information enabling the bacteria to block the action of drugs. Restriction enzymes can slow or halt this absorption process. Enzymes that work in this way are believed to have evolved as a defence mechanism for bacteria.

The researchers also studied the enzyme in action by reacting it with DNA from another organism. They were able to model the mechanism by which the enzyme disables the foreign DNA, while safeguarding the bacteria's own genetic material. Restriction enzymes' ability to sever genetic material is widely applied by scientists to cut and paste strands of DNA in genetic engineering.

The study was carried out in collaboration with the Universities of Leeds and Portsmouth with partners in Poland and France. It was supported by the Biotechnology and Biological Sciences Research Council and the Wellcome Trust and published in Genes and Development journal.

Dr David Dryden, of the University of Edinburgh's School of Chemistry, who led the study, said: "We have known for some time that these enzymes are very effective in protecting bacteria from attack by other species. Now we have painted a picture of how this occurs, which should prove to be a valuable insight in tackling the spread of antibiotic-resistant superbugs."

Provided by University of Edinburgh

'Left-handed iron corkscrews' point the way to new weapon in battle against superbugs like MRSA

Researchers have created a new synthetic class of helix-shaped molecules which they believe could be a key tool in the worldwide battle against antibiotic resistance.

By twisting molecules around iron atoms they have created what they term 'flexicates' which are active against MRSA and E-coli - but which also appear to have low toxicity, reducing the potential for side effects if used in treatment.

The work is published in Nature Chemistry.

The new structures harness the phenomenon of 'chirality' or 'handedness' whereby the corkscrew molecules could be left-handed or right-handed.

By making the most effective 'hand' to attack a specific disease, the University of Warwick research paves the way towards a more targeted approach to killing pathogens.

In the case of E-coli and MRSA, it is the left 'hand' which is most effective.

Professor Peter Scott of the University of Warwick's chemistry department said although this particular study concentrated on flexicates' activity against MRSA and E-coli, the new method of assembly could also result in new treatments for other diseases.

"It's a whole new area of chemistry that really opens up the landscape to other practical uses.

"These new molecules are synthetically flexible, which means that with a bit of tweaking they can be put to use against a whole host of different diseases, not just bugs like MRSA which are rapidly developing resistance to traditional antibiotics.

"Flexicates are also easier to make and produce less waste than many current antibiotics."

Scientists have long been able to copy nature's corkscrew-shaped molecules in man-made structures known as helicates – but they have thus far not been able to use them in fighting diseases.

One of the key issues is the problem of handedness.

Sometimes 'left-handed' molecules in drugs are the most effective at combating some disease, while sometimes the 'right-handed' version works best.

Until now, scientists working with helicates have found it difficult to make samples containing just one type of corkscrew; either the right- or left-handed twist.

But with flexicates, the University of Warwick scientists have succeeded in making samples containing just one type of twist – resulting in a more targeted approach which would allow the drug dosage to be halved.

And flexicates solve other problems encountered by helicates, as they are easier to optimise for specific purposes, are better absorbed by the body and are also easier to mass-produce synthetically.

Professor Scott said: "Drugs often have this property of handedness - their molecules can exist in both right and left handed versions but the body prefers to use only one of them."

"For this reason, drug companies have to go to the trouble of making many traditional molecules as one hand only.

"What we have done is solve the 'handedness' problem for this new type of drug molecule.

"By getting the correct hand we can halve the drug dose, which has the benefits of minimising side effects and reducing waste.

"For patients, it's safer to swallow half the amount of a drug.

"Our work means that we can now make whichever hand of the corkscrew we want, depending on the job we require it to do."

More information: The study, entitled Optically pure, water-stable metallo-helical 'flexicate' assemblies with antibiotic activity, is published in Nature Chemistry. http://dx.doi.org/ … 8/NCHEM.1206

Provided by University of Warwick (news : web)

Decoding the proteins behind drug-resistant superbugs

Penicillin and its descendants once ruled supreme over bacteria. Then the bugs got stronger, and hospitals have reported bacterial infections so virulent that even powerful antibiotics held in reserve for these cases don't work.

To create the next line of defense against the most drug-resistant pathogens, scientists at the U.S. Department of Energy's Argonne National Laboratory and Texas A&M University have decoded the structure of a protein that confers drug resistance against our best antibiotics. The work could provide the foundation for new treatments to fight emerging drug-resistant superbugs.

ß-lactam antibiotics are the most widely used antibacterials in the world because they effectively kill bacteria, but are minimally toxic to human cells—which means they have few side effects. But 1999 sounded the end of the reign of ß-lactams. That year, a patient died in a Swedish hospital from an infection that didn't respond to antibiotics.

Penicillin was the original ß-lactam, but as bugs evolved to fight it, scientists developed an entire family of related antibiotics, including amoxicillin, cephalexin and imipenem. The drugs work by blocking the bacteria's cell walls from growing normally. The latest class, called carbapenems, is generally held as the last line of defense against the toughest drug-resistant infections, like MRSA.

But bugs resistant even to carbapenems have begun spreading across the world, and they can trade this ability not only among each other but to other species of bacteria as well.

Scientists tracked down a gene that allows bacteria to resist these antibiotics, called NDM-1. The gene codes for a protein that latches onto part of the antibiotic molecule: the ß-lactam ring that gives the family its name. The rings are rigid, and once they break apart, the antibiotic is useless. "That's why bacteria with NDM-1 genes are so deadly,” explained Andrzej Joachimiak, an Argonne Distinguished Fellow who co-authored the study.

But NDM-1's greatest trick is that it can disable the entire spectrum of ß-lactam antibiotics. Each different antibiotic has a different molecular structure. Argonne researchers needed to know how one protein could break the rings in a dozen different configurations.

Joachimiak, who has a joint appointment with Argonne and the University of Chicago, took up the challenge with colleagues at the Midwest Center for Structural Genomics and Texas A&M University.

One of the most powerful tools in a biologist's kit is protein crystallography, which zooms down to the molecular level to get a picture of what the protein looks like. Protein crystals are tiny things: a thousand of them could sit side by side in a human hair. But intense X-rays from large synchrotrons like Argonne's Advanced Photon Source can be used as a "camera”: detectors collect the data from X-rays bouncing off the crystallized protein and use it to reconstruct the enzyme's structure, atom by atom.

The team managed to capture the NDM-1 enzyme in three different states. They found that NDM-1's active site, where it latches onto the antibiotic, is abnormally enormous, and flexible—like a mouth that is so large that it can capture the rings from a dozen different antibiotics, no matter their shape.

Decoding the structure allows scientists and companies to study the molecule for weaknesses: places where the structure could be attacked to disrupt its function. Joachimiak and the team are already beginning another study to test one way to neutralize the enzyme.

The study, "Structure of Apo- and Monometalated Forms of NDM-1—A Highly Potent Carbapenem-Hydrolyzing Metallo-ß-Lactamase”, was funded by the National Institutes of Health and has been published online in the journal PLoS ONE</i>.

Provided by Argonne National Laboratory (news : web)