Genetic, biochemical, and structural studies of biogenesis of adhesive pili in bacteria

This chapter discusses how the molecular details of pilus biogenesis, including the roles of pilus subunits and accessory proteins, have been studied using a powerful blend of genetics, biochemistry, carbohydrate chemistry, X-ray crystallography, and high-resolution electron microscopy techniques; and focuses on the P-pilus system as a model for a detailed analysis of postsecretional assembly. Pathogenic organisms appear to have an abundant repertoire of adhesive organelles, probably only a fraction of which have been identified. The different architectures of pill represent a variety of strategies that these pathogens have evolved to adhere effectively to host tissues. Although the minor and major pilus subunits have a diversity of function, interestingly, they are incorporated into adhesive structures using common mechanisms of assembly. The ongoing efforts to identify, isolate, and analyze products of pilin gene clusters will undoubtedly lead to the discovery of additional, highly related members of the immunoglobulin-like chaperone family and the outer membrane usher family, and the discovery of a seemingly diverse group of minor pilin subunits. The sequence comparisons of the pilus chaperone family have highlighted highly conserved amino acid residues which may be critical to chaperone function. Site-directed mutations in these residues have indicated that residues within the cleft are critical to the ability of the chaperone to bind pilus subunits.