THE CRYSTAL-STRUCTURE OF A TRIACYLGLYCEROL LIPASE FROM PSEUDOMONAS-CEPACIA REVEALS A HIGHLY OPEN CONFORMATION IN THE ABSENCE OF A BOUND INHIBITOR

Background: Lipases, a family of enzymes which catalyze the hydrolysis of triglycerides, are widely distributed in many organisms. True lipa ses are distinguished from esterases by the characteristic interfacial activation they exhibit at an oil-water interface. Lipases are one of the most frequently used biocatalysts for organic reactions performed under mild conditions, Their biotechnological applications include fo od and oil processing and the preparation of chiral intermediates for the synthesis of enantiomerically pure pharmaceuticals. Recent structu ral studies on several lipases have provided some clues towards unders tanding the mechanisms of hydrolytic activity, interfacial activation, and stereoselectivity. This study was undertaken in order to provide structural information on bacterial lipases, which is relatively limit ed in comparison to that on the enzymes from other sources. Results: W e have determined the crystal structure of a triacylglycerol lipase fr om Pseudomonas cepacia (Pet) in the absence of a bound inhibitor using X-ray crystallography, The structure shows the lipase to contain an a lpha/beta-hydrolase fold and a catalytic triad comprising of residues Ser87, His286 and Asp264. The enzyme shares several structural feature s with homologous lipases from Pseudomonas glumae (PgL) and Chromobact erium viscosum (CvL), including a calcium-binding site, The present st ructure of Pet reveals a highly open conformation with a solvent-acces sible active site, This is in contrast to the structures of PgL and Pe t in which the active site is buried under a closed or partially opene d 'lid', respectively. Conclusions: Pet exhibits some structural featu res found in other lipases. The presence of the Ser-His-Asp catalytic triad, an oxyanion hole, and the opening of a helical lid suggest that this enzyme shares the same mechanisms of catalysis and interfacial a ctivation as other lipases. The highly open conformation observed in t his study is likely to reflect the activated form of the lipase at an oil-water interface. The structure suggests that the interfacial activ ation of bacterial lipases involves the reorganization of secondary st ructures and a large movement of the lid to expose the active site, Th is is similar to the mechanism described for other well characterized fungal and mammalian lipases.