Remodeling of the Chlamydia psittaci inclusion by the type III secreted, BAR domain-containing inclusion membrane protein IncA
AuthorPhillips, Daniel Austin
AdvisorBavoil, Patrik M.
MetadataShow full item record
AbstractChlamydia species cause infections in humans that range from prevalent, often asymptomatic genital infections caused by Chlamydia trachomatis to relatively rare, potentially life-threatening zoonotic infections caused by avian Chlamydia psittaci. All Chlamydia spp. encode integral membrane proteins (Incs) that are type III-secreted through the injectisome from the bacterial cell into the host-derived inclusion membrane where they interact with host proteins. These include Incs of C. trachomatis that interact with membrane curvature-inducing BAR-domain sorting nexins (SNX), potentially disrupting retromer-mediated endosome-to-Golgi trafficking to benefit the pathogen. Eukaryotic BAR domain proteins interact with bacterial proteins, but prokaryotic BAR domain proteins have yet to be confirmed. I propose that IncA/Cps, the first BAR protein described in a prokaryote, specifically contributes to the remodeling of the C. psittaci inclusion membrane to form a) IncA-laden retromer-like tubules extending outward into the cytosol, and/or b) folds and tubular extensions extending inward into the inclusion lumen. IncA of C. psittaci (IncA/Cps) contains a predicted SNX-BAR-like domain that is absent in the C. trachomatis ortholog. Comparative sequence analysis of IncA orthologs across Chlamydia spp. suggests that the SNX-BAR-like domain of IncA/Cps was acquired by convergent evolution. IncA/Cps BAR-mediated in vitro tubulation of liposomes was observed. Transfected HEK293 cells expressed filamentous/tubular structures laden with IncA/Cps. These observations suggest that IncA/Cps has membrane remodeling activity. During C. psittaci infection, IncA/Cps localized to the inclusion membrane and to nocodazole-sensitive retromer-like tubules extending from the inclusion membrane into the host cytosol. IncA-specific immunofluorescence staining of the C. psittaci inclusion displayed a characteristic irregular configuration with concave pits and folds extending into the inclusion lumen, sharply contrasting the characteristic ovoid shape of the C. trachomatis inclusion. In addition, abundant luminal IncA/Cps staining did not colocalize with growing chlamydiae and was sensitive to host sphingolipid biosynthesis inhibition. This suggests that luminal IncA/Cps is structurally continuous with the inclusion membrane. Inward extensions may enhance inclusion membrane contact-dependent growth of C. psittaci and eventually infectious progeny per infected cell. The higher infectious load may contribute to C. psittaci-induced severe pathologies and high transmission rates between birds and to humans.
DescriptionUniversity of Maryland, Baltimore. Molecular Microbiology and Immunology. Ph.D. 2016
Type III Secretion Systems