title: Chlamydia trachomatis polymorphic membrane protein D is an oligomeric autotransporter with a higher-order structure.
abstract: Chlamydia trachomatis is a globally important obligate intracellular bacterial pathogen that is a leading cause of sexually transmitted disease and blinding trachoma. Effective control of these diseases will likely require a preventative vaccine. C. trachomatis polymorphic membrane protein D (PmpD) is an attractive vaccine candidate as it is conserved among C. trachomatis strains and is a target of broadly cross-reactive neutralizing antibodies. We show here that immunoaffinity-purified native PmpD exists as an oligomer with a distinct 23-nm flower-like structure. Two-dimensional blue native-sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses showed that the oligomers were composed of full-length PmpD (p155) and two proteolytically processed fragments, the p73 passenger domain (PD) and the p82 translocator domain. We also show that PmpD undergoes an infection-dependent proteolytic processing step late in the growth cycle that yields a soluble extended PD (p111) that was processed into a p73 PD and a novel p30 fragment. Interestingly, soluble PmpD peptides possess putative eukaryote-interacting functional motifs, implying potential secondary functions within or distal to infected cells. Collectively, our findings show that PmpD exists as two distinct forms, a surface-associated oligomer exhibiting a higher-order flower-like structure and a soluble form restricted to infected cells. We hypothesize that PmpD is a multifunctional virulence factor important in chlamydial pathogenesis and could represent novel vaccine or drug targets for the control of human chlamydial infections.
authors.affiliation: Laboratory of Intracellular Parasites, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 903 South 4th St., Hamilton, MT 59840, USA.
authors.forename: Kena A
authors.initials: KA
authors.lastname: Swanson
authors.forename: Lacey D
authors.initials: LD
authors.lastname: Taylor
authors.forename: Shaun D
authors.initials: SD
authors.lastname: Frank
authors.forename: Gail L
authors.initials: GL
authors.lastname: Sturdevant
authors.forename: Elizabeth R
authors.initials: ER
authors.lastname: Fischer
authors.forename: John H
authors.initials: JH
authors.lastname: Carlson
authors.forename: William M
authors.initials: WM
authors.lastname: Whitmire
authors.forename: Harlan D
authors.initials: HD
authors.lastname: Caldwell
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D002692:Chlamydia trachomatis / Q000737:chemistry* / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D004847:Epithelial Cells / Q000737:chemistry / Q000382:microbiology; D006367:HeLa Cells; D006801:Humans; D018613:Microscopy, Confocal; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D010447:Peptide Hydrolases / Q000737:chemistry / Q000378:metabolism; D055503:Protein Multimerization
chemical_list: D001425:Bacterial Outer Membrane Proteins; C484024:polymorphic membrane protein 21, Chlamydophila pneumoniae; D010447:Peptide Hydrolases