PASADENA, Calif.Bacteria have evolved different systems for secreting proteins into the fluid around them or into other cells. Some, for example, have syringe-like exterior structures that can pierce other cells and inject proteins. Another system, called a type VI secretion system, is found in about a quarter of all bacteria with two membranes. Despite being common, researchers have not understood how it works. Now a team, co-led by researchers at the California Institute of Technology (Caltech), has figured out the structure of the type VI secretion system apparatus and proposed how it might workby shooting spring-loaded poison molecular daggers.
"People aren't surprised that animals have really interesting ways to hurt each othersnakes have venom, bears have claws," says Grant Jensen, professor of biology at Caltech and coleader of the study. "But they might be surprised that a single cell within one of those animals' bodies is still 100 times larger than the bacterial cells we're talking about, and yet the bacterial cells contain weapons that are so sophisticated. That's the marvel."
The nano-weaponwhich spans a distance no longer than about 80 atoms lined up end-to-endis a tube that contracts very quickly, firing an inner dagger through the cell's membranes, into the surrounding medium and, possibly, into another cell. The tube then disassembles and can reassemble elsewhere in the cell, ready to fire another molecular dagger.
The findings, made in collaboration with researchers at Harvard Medical School, appear as an advance online publication of the journal Nature.
The work began with an accidental discovery. Researchers in the Jensen lab were using an electron cryomicroscopean electron microscope that enables researchers to observe samples in a near-native stateto image an environmental strain of Vibrio cholerae cells. Unlike traditional electron microscopyfor which samples must be fixed, dehydrated, e
|Contact: Deborah Williams-Hedges|
California Institute of Technology