Pilus biogenesis via the chaperone/usher pathway: an integration of structure and function

The molecular basis of how pathogenic bacteria cause disease has been studied by blending a well-developed genetic system with X-ray crystallography, protein chemistry, high resolution electron microscopy, and cell biology. Microbial attachment to host tissues is one of the key events in the early stages of most bacterial infections. Attachment is typically mediated by adhesins that are assembled into hair-like fibers called pili on bacterial surfaces. This article focuses on the structure-function correlates of P pili, which are produced by most pyelonephritic strains of Escherichia coli. P pili are assembled via a chaperone/usher pathway. Similar pathways are responsible for the assembly of over 30 adhesive organelles in various Gram-negative pathogens. P pilus biogenesis has been used as a model system to elucidate common themes in bacterial pathogenesis, namely, the protein folding, secretion, and assembly of virulence factors. The structural basis for pilus biogenesis is discussed as well as the function and consequences of microbial attachment.