Bacterial Export Machine Unveiled

When gram-negative bacteria want to share useful genes with other bacteria, many of them use the so-called type IV secretion complex to export the genes from their cytoplasm to the outside world. This secretion machinery is how bacteria are able to develop antibiotic resistance or start metabolizing a new energy source. A variety of pathogens that cause everything from ulcers to whooping cough also use the export machinery to deliver toxic proteins into their hosts. In addition, scientists have co-opted the type IV secretion complex of plant-infecting bacteria to deliver DNA to create genetically modified crops. Now, a research group led by Gabriel Waksman of Birkbeck College, in London, and University College London is reporting a first peek at the structure of the mammoth 1.1-megadalton protein complex (Science 2009, 323, 266). The rough-grain, 15-Å structure, which the researchers obtained by cryo-electron microscopy, will hopefully inform efforts to crystallize the 42 proteins that form the complex, Waksman says. "Our hope is that we can eventually target new small molecules that inhibit the secretion process during infection by pathogens," he adds.