Bacterial protein mimics its host to disable a key enzyme (w/ Video)

December 11, 2009

( -- Bacteria use all sorts of cunning to trick hosts into doing their bidding. One con in their bag of tricks: the molecular mimic. In this ruse, bacteria or their agents look for all purposes like some native molecule in a cell, but then do not behave accordingly. Working with H. pylori, the bacterium responsible for gastric ulcers and cancer, researchers have revealed one way bacteria pull this off, deciphering the structure of a piece of CagA, a bacterial protein that impersonates a human protein in order to disable a key enzyme.

Helicobacter pylori infects up to 90 percent of people in the developing world and causes gastric ulcers and cancers of the gut. Now scientists have revealed a subterfuge used by the to trick into playing along. By injecting a protein into the stomach lining that mimics a native protein but has its opposite effect, the bacterium shuts down a process that helps properly structure stomach tissue, scientists say.

C. Erec Stebbins, head of the Laboratory of Structural Microbiology at Rockefeller University, Research Associate Dragana Nesic and colleagues deciphered the of an important segment of the large H. pylori protein CagA as it attached to a human enzyme called MARK2. MARK2 (also known as PAR1b) regulates processes including the “tight junctions” that form between cells, packing stomach tissue together. Using the technique of x-ray crystallography, the researchers captured CagA bound to MARK2 and established the position of each atom surrounding the interaction by interpreting the pattern of x-rays diffracting from a crystallized structure of the union.

The team, including biomedical fellow Marshall Miller and Brian T. Chait’s Laboratory of and Gaseous Ion Chemistry, published the experiments December 6 in Nature Structural & Molecular Biology. “It was the first time anyone has ever imaged CagA interacting with a human protein,” Stebbins says. “We know CagA basically shuts down MARK2, disrupting different cell functions, and we wanted to find out how that happens. We start with structure and move on to function.”

The researchers performed a series of biochemical tests, creating CagA mutants missing individual amino acid residues to determine which ones are crucial to its interaction with MARK2. Nesic identified four key elements in a “binding pocket” of the protein in an arrangement that is strikingly similar to many of the body’s native proteins that interact with MARK2. “Evolution has created a — CagA — that looks exactly like one of ours, and the enzyme that interacts with it is totally fooled,” Stebbins says. “CagA binds to it so tightly that the enzyme gets locked in this trapped, dead state and is unable to do what it usually would.”

The work by Nesic and Stebbins looks at only one part of the large protein, but their success in detailing the structure and function of this important element shows that it’s possible to dissect the protein one piece at a time. H. pylori is known for its direct involvement in gastric ulcers and tumors, and the activity of the enzyme that CagA effectively shuts down has been implicated in other disorders, including Alzheimer’s disease and obesity. So understanding more about how CagA works is potentially useful for treating a litany of medical problems.

“What we hope is that now we’ve opened up CagA by showing how we can take this huge on,” Stebbins says. “We would love to see this kind of research accelerate because there is a lot more we need to understand about how it works.”

More information: Nature Structural & Molecular Biology online: December 6, 2009; CagA inhibits PAR1-MARK family kinases by mimicking host substrates; Dragana Nesic, Marshall C. Miller, Zachary T. Quinkert, Markus Stein, Brian T. Chait and C. Erec Stebbins

Provided by Rockefeller University (news : web)

Explore further: Helicobacter pylori inhibits intercellular communication of cultured gastric cells

Related Stories

H. Pylori bacteria may help prevent some esophageal cancers

October 6, 2008

Some bacteria may help protect against the development of a type of esophageal cancer, known as adenocarcinoma, according to a new review of the medical literature. These bacteria, which are called Helicobacter pylori, live ...

What is the risk factor for gastric cancer in a Costa Rican?

January 21, 2009

A research group from Costa Rican evaluated risk factors for gastric cancer in Costa Rican regions with contrasting gastric cancer incidence rates (GCIR). They found that although a pro-inflammatory cytokine genetic profile ...

Structural study of anthrax yields new antibiotic target

January 28, 2008

Researchers studying anthrax knew they were onto something when they discovered an opponent the bacterium couldn’t outwit. Probing a bit deeper, they discovered this was because the attacker was interacting with something ...

Recommended for you

Stressed-out meerkats less likely to help group

September 22, 2017

Dominant female meerkats use aggression to keep subordinates from breeding, but a new study finds this negative behavior also can result in the latter becoming less willing to help within the group.

Why poison frogs don't poison themselves

September 21, 2017

Don't let their appearance fool you: Thimble-sized, dappled in cheerful colors and squishy, poison frogs in fact harbor some of the most potent neurotoxins we know. With a new paper published in the journal Science, scientists ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Dec 13, 2009
Great Article..very nice to have the video..the guys there are doing a great job!!!!...Im sure this will open the doors to more research with similar pathogens.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.