Expression, purification, crystallization and preliminary X-ray studies of the outer membrane efflux proteins OprM and OprN from Pseudomonas aeruginosa

OprM and OprN belong to the outer membrane factor family proteins. These approximately 52 kDa proteins are part of the tripartite efflux pumps found in Pseudomonas aeruginosa and are responsible in part for the antibiotic resistance observed in these bacteria. Both proteins have been expressed in Escherichia coli as His-tag proteins and purified accordingly by affinity chromatography in the presence of n-octyl-beta-D-glucopyranoside detergent. OprM and OprN were crystallized using PEG 20 000/ammonium citrate and ammonium sulfate as precipitating agents, respectively. Crystals belong to space group C2, with unit-cell parameters a = 152.6, b = 87.9, c = 355.9 A, beta = 98.9 degrees and a = 151.3, b = 87.6, c = 356.5 A, beta = 98.1 degrees for OprM and OprN, respectively. Using the ESRF synchrotron-radiation source, OprM diffraction data extended to 3.4 A.