Nearly a billion years ago, bacteria evolved an insidious means of infecting their hosts - a syringe-like mechanism able to inject cells with stealthy hijacker molecules. These molecules, called virulence factors, play a sophisticated game of mimicry, imitating many of the cells' normal activities but ultimately co-opting them to serve the bacteria's needs.
Now researchers at The Rockefeller University have identified a new class of these coup artists that appear to take over a key process that regulates a wide range of cellular duties, from cell-cycle progression to cell death, even communication between cells.
Scientists in C. Erec Stebbins's Laboratory of Structural Microbiology have discovered the crystal structure of virulence factor SspH2, which is deployed by Salmonella, a mean strain of bacteria that can cause food poisoning, typhoid
fever and septicemia. With colleagues at Yale University, they performed a series of biochemical experiments to show that SspH2 is an enzyme that links two molecules together, called a ligase. Specifically, it is involved in the targeting of a widespread regulatory molecule called ubiquitin to other proteins. Ubiquitin's most common function is to label proteins for degradation in a process called ubiquitination.
"It's a totally new ubiquitin ligase from a bacterial pathogen going in and messing around with human cell chemistry," says Stebbins. "It's a good example of the amazing ways bacteria have found to play around with our biochemistry for its own purposes."