Journal
EMBO JOURNAL
Volume 25, Issue 15, Pages 3702-3713Publisher
WILEY
DOI: 10.1038/sj.emboj.7601237
Keywords
2D crystallization; membrane protein; protein function; X-ray crystallography
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OmpG, a monomeric pore-forming protein from Escherichia coli outer membranes, was refolded from inclusion bodies and crystallized in two different conformations. The OmpG channel is a 14-stranded beta-barrel, with short periplasmic turns and seven extracellular loops. Crystals grown at neutral pH show the channel in the open state at 2.3 angstrom resolution. In the 2.7 angstrom structure of crystals grown at pH 5.6, the pore is blocked by loop 6, which folds across the channel. The rearrangement of loop 6 appears to be triggered by a pair of histidine residues, which repel one another at acidic pH, resulting in the breakage of neighbouring H-bonds and a lengthening of loop 6 from 10 to 17 residues. A total of 151 ordered LDAO detergent molecules were found in the 2.3 angstrom structure, mostly on the hydrophobic outer surface of OmpG, mimicking the outer membrane lipid bilayer, with three LDAO molecules in the open pore. In the 2.7 angstrom structure, OmpG binds one OG and one glucose molecule as sugar substrates in the closed pore.
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