Structure of a pilin monomer from Pseudomonas aeruginosa - Implications for the assembly of pili

Type TV pilin monomers assemble to form fibers called pill that are require d far a variety of bacterial functions. Pilin monomers oligomerize due to t he interaction of part of their hydrophobic N-terminal alpha -helix. Engine ering of a truncated pilin from Pseudomonas aeruginosa strain K122-4, where the first 28 residues are removed from the N terminus, yields a soluble, m onomeric protein. This truncated pilin is shown to bind to its receptor and to decrease morbidity and mortality in mice upon administration 15 min bef ore challenge with a heterologous strain of Pseudomonas. The structure of t his truncated pilin reveals an alpha -helix at the N terminus that lies acr oss a 4-stranded antiparallel beta -sheet. A model for a pilus is proposed that takes into account both electrostatic and hydrophobic interactions of pilin subunits as well as previously published x-ray fiber diffraction data . Our model indicates that DNA or RNA cannot pass through the center of the pilus, however, the possibility exists for small organic molecules to pass through indicating a potential mechanism for signal transduction.