Active-site architecture and catalytic mechanism of the lipid A deacylase LpxR of Salmonella typhimurium.
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Rutten L, Mannie JP, Stead CM, Raetz CR, Reynolds CM, Bonvin AM, Tommassen JP, Egmond MR, Trent MS, Gros P
Active-site architecture and catalytic mechanism of the lipid A deacylase LpxR of Salmonella typhimurium.
Proc Natl Acad Sci U S A. 2009 Feb 10;106(6):1960-4. doi: 10.1073/pnas.0813064106. Epub 2009 Jan 27.
- PubMed ID
- 19174515 [ View in PubMed]
- Abstract
The lipid A portion of lipopolysaccharide, the major component of the outer leaflet of the outer membrane of gram-negative bacteria, is toxic to humans. Modification of lipid A by enzymes often reduces its toxicity. The outer-membrane protein LpxR from Salmonella typhimurium is a lipid A-modifying enzyme. It removes the 3'-acyloxyacyl moiety of the lipid A portion of lipopolysaccharide in a Ca(2+)-dependent manner. Here, we present the crystal structure of S. typhimurium LpxR, crystallized in the presence of zinc ions. The structure, a 12-stranded beta-barrel, reveals that the active site is located between the barrel wall and an alpha-helix formed by an extracellular loop. Based on site-directed mutagenesis and modeling of a substrate on the active site, we propose a catalytic mechanism similar to that of phospholipase A2, in which a Ca(2+) forms the oxyanion hole and a histidine activates a water molecule (or a cascade of two water molecules) that subsequently attacks the carbonyl oxygen of the scissile bond.