title: Structural biology of membrane-intrinsic beta-barrel enzymes: sentinels of the bacterial outer membrane.
abstract: The outer membranes of Gram-negative bacteria are replete with integral membrane proteins that exhibit antiparallel beta-barrel structures, but very few of these proteins function as enzymes. In Escherichia coli, only three beta-barrel enzymes are known to exist in the outer membrane; these are the phospholipase OMPLA, the protease OmpT, and the phospholipidColon, two colonslipid A palmitoyltransferase PagP, all of which have been characterized at the structural level. Structural details have also emerged for the outer membrane beta-barrel enzyme PagL, a lipid A 3-O-deacylase from Pseudomonas aeruginosa. Lipid A can be further modified in the outer membrane by two beta-barrel enzymes of unknown structure; namely, the Salmonella enterica 3'-acyloxyacyl hydrolase LpxR, and the Rhizobium leguminosarum oxidase LpxQ, which employs O(2) to convert the proximal glucosamine unit of lipid A into 2-aminogluconate. Structural biology now indicates how beta-barrel enzymes can function as sentinels that remain dormant when the outer membrane permeability barrier is intact. Host immune defenses and antibiotics that perturb this barrier can directly trigger beta-barrel enzymes in the outer membrane. The ensuing adaptive responses occur instantaneously and rapidly outpace other signal transduction mechanisms that similarly function to restore the outer membrane permeability barrier.
authors: Department of Biochemistry and Biomedical Sciences, 1200 Main Street West, Health Sciences Centre 4H19, McMaster University, Hamilton, ON, Canada L8N 3Z5. bishopr@mcmaster.ca
authors: Russell E
authors: RE
authors: Bishop
mesh_terms: D000217:Acyltransferases / Q000737:chemistry / Q000502:physiology; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D001426:Bacterial Proteins / Q000737:chemistry / Q000502:physiology; D002265:Carboxylic Ester Hydrolases / Q000737:chemistry / Q000502:physiology; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D004926:Escherichia coli / Q000737:chemistry / Q000201:enzymology; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000502:physiology; D006090:Gram-Negative Bacteria / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism / Q000648:ultrastructure; D008954:Models, Biological; D008958:Models, Molecular; D054466:Phospholipases A1 / Q000737:chemistry / Q000502:physiology; D018272:Porins / Q000737:chemistry / Q000502:physiology; D011487:Protein Conformation; D017433:Protein Structure, Secondary
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D018272:Porins; C405564:ompT protein, bacteria; D000217:Acyltransferases; D002265:Carboxylic Ester Hydrolases; D054466:Phospholipases A1