Structural biology of membrane-intrinsic beta-barrel enzymes: sentinels of the bacterial outer membrane.
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.
Bishop
Russell E
RE
Department of Biochemistry and Biomedical Sciences, 1200 Main Street West, Health Sciences Centre 4H19, McMaster University, Hamilton, ON, Canada L8N 3Z5. bishopr@mcmaster.ca
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
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