HAEMOPHILUS-INFLUENZAE PILI ARE COMPOSITE STRUCTURES ASSEMBLED VIA THE HIFB CHAPERONE

Haemophilus influenzae is a Gram-negative bacterium that represents a common cause of human disease. Disease due to this organism begins wit h colonization of the upper respiratory mucosa, a process facilitated by adhesive fibers called pill. In the present study, we investigated the structure and assembly of H. influenzae pill. Examination of pill by electron microscopy using quick-freeze, deep-etch and immunogold te chniques revealed the presence of two distinct subassemblies, includin g a flexible two-stranded helical rod comprised of HifA and a short, t hin, distal tip structure containing HifD. Genetic and biochemical stu dies demonstrated that the biogenesis of H. influenzae pill is depende nt on a periplasmic chaperone called HifB, which belongs to the PapD f amily of immunoglobulin-like chaperones. HifB bound directly to HifA a nd HifD, forming HifB-HifA and HifB-HifD complexes, which were purifie d from periplasmic extracts by ion-exchange chromatography. Continued investigation of the biogenesis of H. influenzae pill should provide g eneral insights into organelle development and may suggest novel strat egies for disease prevention.