Outer membrane protein A

UniProtKB accession:  P0A910

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UniProtKB description:  With TolR probably plays a role in maintaining the position of the peptidoglycan cell wall in the periplasm (Probable). Plays a role in resistance to environmental stress, and a role in outer membrane functionality and cell shape (PubMed:11906175, PubMed:361695). Non-covalently binds peptidoglycan (PubMed:25135663) (Probable). Acts as a porin with low permeability that allows slow penetration of small solutes (PubMed:1370823, PubMed:20004640, PubMed:21069910). A very abundant protein, there can be up to 210,000 OmpA molecules per cell (PubMed:24766808). Reconstitution in unilamellar lipid vesicles shows only about 3% of the protein is in an open conformation, which allows diffusion of L-arabinose at a rate comparable to that of OmpF porin; the pores interconvert very rarely (PubMed:7517935). Native and reconstituted protein forms ion channels with 2 conductance states of (50-80 pS) and (260-320 pS); the states are interconvertible in this study. Interconversion requires refolding of the periplasmic domain (PubMed:10636850). Small pores are converted into large pores by increasing temperature; in this model the C-terminal periplasmic domain forms 8 more beta sheets to form a larger pore (PubMed:15850404). The center of the isolated beta-barrel is polar and has a central gate (involving Glu-73, Lys-103, Glu-149 and Arg-159, sandwiched between Tyr-29, Phe-40 and Tyr-94), with no obvious passage for water or ions (PubMed:9808047) (Probable). Gating involves the Glu-73-Arg-159 salt bridge; gate opening probably involves formation of alternate salt bridges Glu-149-Arg-159 and Glu-73-Lys-103 (PubMed:17041590). Modeling suggests that non-covalent binding of OmpA (from the outer membrane) and TolR (from the inner membrane) to peptidoglycan maintains the position of the cell wall in the periplasm, holding it approximately equidistant from both the inner and outer membranes. Trimeric Lpp controls the width of the periplasm, adjusts its tilt angle to accommodate to the available space, and can compensate in part for an absence of OmpA (Probable).