MOLECULAR-BASIS OF 2 SUBFAMILIES OF IMMUNOGLOBULIN-LIKE CHAPERONES

The initial encounter of a microbial pathogen with the host often invo lves the recognition of host receptors by different kinds of bacterial adhesive organelles called pill, fimbriae, fibrillae or afimbrial adh esins. The development of over 26 of these architecturally diverse adh esive organelles in various Gram-negative pathogens depends on peripla smic chaperones that are comprised of two immunoglobulin-like domains. All of the chaperones possess a highly conserved sheet in domain 1 an d a conserved interdomain hydrogen-bonding network. Chaperone-subunit complex formation depends on the anchoring of the carboxylate group of the subunit into the conserved crevice of the chaperone cleft and the subsequent positioning of the COOH terminus of subunits along the exp osed edge of the conserved sheet of the chaperone. We discovered that the chaperones can be divided into two distinct subfamilies based upon conserved structural differences that occur in the conserved sheet. I nterestingly, a subdivision of the chaperones based upon whether they assemble rod-like pill or non-pilus organelles that have an atypical m orphology defines the same two subgroups. The molecular dissection of the two chaperone subfamilies and the adhesive fibers that they assemb le has advanced our understanding of the development of virulence-asso ciated organelles in pathogenic bacteria.