Architecture of the cell envelope of Chlamydia psittaci 6BC

Abstract

The cysteine-rich envelope proteins of the elementary body form of chlamydiae are thought to be located in the outer membrane on the basis of their insolubility in the weak anionic detergent N-lauryl sarcosinate (Sarkosyl). We found, however, that the insolubility of the small (EnvA) and the large (EnvB) cysteine-rich proteins of Chlamydia psittaci 6BC in Sarkosyl is dependent on the maintenance of a supramolecular disulfidecross-linked complex and is unlikely to be a valid indicator of outer membrane location. Consequently, we used other methods to characterize the architecture of the cell envelope of C. psittaci 6BC. We found that disulfidereduced EnvA, previously shown to be a lipoprotein, segregated into the detergent phase during Triton X-114 partitioning experiments and was recovered from the membrane fraction of elementary bodies lysed by nondetergent means. In contrast, disulfide-reduced EnvB segregated to the aqueous phase in partitioning experiments and was found in the soluble fraction of elementary bodies lysed in the absence of detergents. The hydrophobic affinity probe 3-(trifluoromethyl)-3-(m-[ 125 I]iodophenyl)-diazirine labeled the major outer membrane protein and EnvA but did not label EnvB. Treatment of intact elementary bodies of C. psittaci with trypsin had no effect on the cysteine-rich proteins, although the major outer membrane protein was partially degraded. On the basis of these and other observations, we propose that EnvA is anchored to the outer membrane by its lipid moiety, with a hydrophilic peptide portion extending into the periplasm, and that EnvB is located exclusively within the periplasm. We further propose that disulfide-cross-linked polymers of EnvB are the functional equivalent of peptidoglycan, forming a disulfide-cross-linked network with the periplasmic domains of EnvA and other membrane proteins, which accounts for the osmotic stability of elementary bodies.

Human CD8+ T Cells Recognize the 60-kDa Cysteine-Rich Outer Membrane Protein fromChlamydia trachomatis

“…How it breaches this compartment is unclear, given its hypothesized function. OmcB and OmcA (9-kDa cysteine-rich protein) are postulated to reside in the periplasmic space of EBs and to be functionally associated with the outer membrane complex (41). Both OmcB and OmcA contain numerous cysteine residues and, along with MOMP, may confer rigidity and osmotic integrity to chlamydial EBs by creating a lattice of disulfide bond cross-linked structure, forming the functional equivalent of peptidoglycan (42,43).…”

Simkania negevensis, an insight into the biology and clinical importance of a novel member of the Chlamydiales order

“…These cysteine-rich proteins are sensitive to the redox state of the environment and they might provide some rigidity and resistance to osmotic pressure through the formation of disulfide bridges. Some authors suggested that they may replace the peptidoglycan layer present in the periplasm of other Gram-negative bacteria (Everett & Hatch, 1995;Sun et al, 2007). No homologs of OmcA and OmcB were identified in S. negevensis genome and none of the identified MOMP-like proteins could serve this function as their content in cysteine was extremely low (Aistleitner et al, 2015).…”

Predominant Role of Toll-Like Receptor 2 Versus 4 in Chlamydia pneumoniae-Induced Activation of Dendritic Cells

“…Human diseases attributed to C. pneumoniae include atypical pneumoniae, bronchitis, otitis media, and perhaps arteriosclerosis (5). Structurally, C. pneumoniae displays a cell wall similar to that of Gram-negative bacteria (6). However, two important differences exist.…”