Chlamydia trachomatisPolymorphic 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.Chlamydia trachomatis is a mucosotropic obligate intracellular gram-negative pathogen that is a leading cause of sexually transmitted and ocular infections. Infection can result in serious sequelae such as infertility and blindness (54, 56) and an increased risk of human immunodeficiency virus infection and transmission (38). The pathophysiology of chlamydial infection is associated with the pathogen's propensities to cause persistent infection and to suppress host immunity (3). A vaccine is needed to control chlamydial diseases; however, progress toward this goal will not be forthcoming until more is known about the virulence factors that mediate persistence and immune evasion.Chlamydiae are characterized by a unique biphasic developmental cycle that modulates between an extracellular, metabolically inactive, infectious elementary body (EB) and an intracellular, metabolically active, noninfectious reticulate body (RB) (34). Their obligate intracellular niche and the lack of a tractable genetic system present unique challenges in the study of chlamydial biology and pathogenesis. To overcome these hurdles, chlamydial genomes from a diverse spectrum of hostspecific strains have been sequenced. Comparative genomics have shown considerable homology among various chlamydial species and have provided important insights into shared and species-specific virulence factors (7,24,41,42,46,49).The type V or autotransporter (AT) secretion p...

The Chlamydia pneumoniae Adhesin Pmp21 Forms Oligomers with Adhesive Properties

“…4C). The in vitro formation of Pmp21-D oligomers is in agreement with earlier findings which indicated that the C. trachomatis homologue of Pmp21, PmpD, is part of a protein complex on the EB cell surface (24). Moreover, it was reported that Pmps of Chlamydia psittaci also occur in supramolecular complexes (50).…”

“…Nevertheless, these fungal adhesins form cell surface amyloid patches of arrayed adhesin molecules ("adhesin nanodomains") 100-1000 nm in size, thus binding ligands with high avidity (67,68). It is tempting to speculate that the flower-like structures observed by EM in affinity-enriched preparations of endogenous PmpD-containing protein complexes might possibly represent the in vivo version of the Pmp21 protofibrils detected in vitro in this study (24). The data presented here are compatible with the idea that oligomeric Pmp complexes might enhance the chlamydial cell's capacity for adhesion to human epithelial cells and be important for the initial step in infection.…”

“…Moreover, it has been speculated that Pmp ␤-helices could associate with each other to generate oligomers (20). Like other autotransporter proteins, many Pmps undergo complex proteolytic processing (13,18,(21)(22)(23)(24). Several of the C. pneumoniae and all C. trachomatis Pmps have been shown to be located on the chlamydial surface (10, 13, 18, 21, 22, 24 -26).…”

Biological Characterization ofChlamydia trachomatisPlasticity Zone MACPF Domain Family Protein CT153

“…C. trachomatis serovar L2-infected L929 suspension cultures were harvested by centrifugation at 0, 12, 24, 30, and 36 h postinfection and lysed by Dounce homogenization, and cellular fractionation was performed as previously described (9,18,53). Insoluble and soluble fractions were analyzed by Western blotting using anti-CT153, anti-MOMP, or anti-chlamydial protease-like activity factor (CPAF) (16) Abs.…”

CPAF selectively degrades chlamydial T cell antigens for inhibiting antigen presentation

“…To overcome the host immunity barriers, and establish the successful infection, chlamydia may utilize virulence factors as previously proposed [10]. Many virulence factor candidates have been identified, such as the polymorphic outer membrane autotransporter family of proteins [11,12], the putative large cytotoxin [13], stress response proteins [14], and chlamydial secretion effectors [15][16][17]. It is known that C. trachomatis organisms can secrete numerous proteins into host cell cytoplasm [18,19].…”