
Full text loading...
Category: Bacterial Pathogenesis
The Chlamydial Cell Envelope, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817329/9781555816742_Chap04-1.gif /docserver/preview/fulltext/10.1128/9781555817329/9781555816742_Chap04-2.gifAbstract:
Chlamydial development is punctuated by changes in protein-protein interactions on elementary body (EB) and reticulate body (RB) surfaces. Reduction of disulfide cross-links in the chlamydial outer membrane complex (COMC) concomitant with attachment and entry of the EB is rapidly followed by transition to the fragile RB, which is specialized for acquisition of nutrients during chlamydial growth and differentiation. This chapter reviews knowledge about the progression starting with the structure of the EB envelope in the extracellular environment and the way in which this surface interacts with, and is altered during, the process of chlamydial attachment, entry, development, and exit from host cells. The presence of gram-negative double membranes was confirmed by early transmission electron microscopy (TEM) studies of RBs and EBs, but challenges in purification and fractionation of RB membranes shifted emphasis toward EB membranes in subsequent studies. Regularly spaced hexagonal lattices were observed in negatively stained EB envelope preparations. Hexagonal lattices, located between the outer and cytoplasmic EB membranes, and similar structures were present in multiple Chlamydia species. Varying degrees of evidence suggest that additional EB OMPs may exist. The envelopes of the extracellular EB and intracellular RB differ markedly and reflect requirements for survival of chlamydiae in two unique environments. Outside the cell, the oxidized COMC provides osmotic protection, restricts loss of metabolites across the OM, and may mask immunogenic determinants that could alert host cells to the presence of these pathogens.
Full text loading...
Model of the EB surface. OmcB (dumbbells) and OmcA (triangles) are located primarily in the periplasm. LPS (small gray hexagons) is primarily located in the outer leaflet of the outer membrane, while phospholipids are in the inner leaflet (small open circles). OmcA is associated with the inner leaflet of the OM by its lipid moiety (not shown). An N-terminal portion of some OmcB molecules may traverse the OM and bind HS on the EB surface (chains of open hexagons). HS may also bind unknown residues on MOMP. OmcA and OmcB are cysteine cross-linked to one another in the periplasm, and, speculatively, to other OMPs such as CdsC, PorB, and some Pmps (PmpH and hypothetical PmpX). The figure shows a range of scenarios that may occur for specific Pmps. For example, the passenger domain (shown as ovals for each of the Pmps) of PmpH has been exported to the EB surface, whereas export of the passenger domain of PmpX has not been completed. Export of the hypothetical PmpZ passenger domain has been completed, but its transporter domain is not bound to other COMC proteins. Oligomers of PmpD, which have been processed from their passenger domains, are loosely associated with the surface of the EB. Polymers of the putative T3S needle protein CdsF extend from CdsC. doi:10.1128/9781555817329.ch4.f1
Model of the EB surface. OmcB (dumbbells) and OmcA (triangles) are located primarily in the periplasm. LPS (small gray hexagons) is primarily located in the outer leaflet of the outer membrane, while phospholipids are in the inner leaflet (small open circles). OmcA is associated with the inner leaflet of the OM by its lipid moiety (not shown). An N-terminal portion of some OmcB molecules may traverse the OM and bind HS on the EB surface (chains of open hexagons). HS may also bind unknown residues on MOMP. OmcA and OmcB are cysteine cross-linked to one another in the periplasm, and, speculatively, to other OMPs such as CdsC, PorB, and some Pmps (PmpH and hypothetical PmpX). The figure shows a range of scenarios that may occur for specific Pmps. For example, the passenger domain (shown as ovals for each of the Pmps) of PmpH has been exported to the EB surface, whereas export of the passenger domain of PmpX has not been completed. Export of the hypothetical PmpZ passenger domain has been completed, but its transporter domain is not bound to other COMC proteins. Oligomers of PmpD, which have been processed from their passenger domains, are loosely associated with the surface of the EB. Polymers of the putative T3S needle protein CdsF extend from CdsC. doi:10.1128/9781555817329.ch4.f1