FEATURES

FAMILY

outer membrane factor (OMF) (TC 1.B.17) family

DESCRIPTION

Also known as OPRM_PSEAE, oprM, oprK. The outer membrane component of the MexAB-OprM efflux system that confers multidrug resistance. Also functions as the major efflux pump for n-hexane and p-xylene efflux. Over-expression of the pump increases antibiotic and solvent efflux capacities. Can replace the OprJ outer membrane component of the MexCD-OprJ pump; the antibiotics exported are those exported by the intact MexCD pump, showing that efflux substrate specificity is not conferred by this component. Serves as the outer membrane component for the MexXY efflux system. Implicated in the secretion of the siderophore pyoverdine. OprM is probably involved in the efflux of the siderophore across the outer membrane., The ability to export antibiotics and solvents is dramatically decreased in the presence of the proton conductor carbonyl cyanide m-chlorophenylhydrazone (CCCP), showing that an energized inner membrane is required for efflux. It is thought that the MexB subunit is a proton antiporter. Component of the MexAB-OprM multidrug efflux complex composed of an unknown number of MexA subunits, MexB and an OprM homotrimer. The OprM homotrimer assembles to form a 135 Angstroms-long pore. It consists of a beta-barrel, which is probably inserted in the outer membrane, and an alpha-barrel formed by alpha-helices which probably spans the periplasm. In the ground state the periplasmic end is closed, while the outer membrane end opening is 6-8 Angstroms in diameter. The OprM trimer is thought to contact the inner membrane MexB transporter. The MexA subunits are thought to form a barrel which allows substrates to pass directly from the cytoplasm to the external mileu. How the MexA subunits interact with OprM and MexB, and how the OprM channel is opened is unknown.

EXTERNAL LINKS

oprM

Outer membrane protein OprM

oprM

Molecular Synopsis