Crystal structure of Pseudomonas aeruginosa lipase in the open conformation - The prototype for family I.1 of bacterial lipases

The x-ray structure of the lipase from Pseudomonas aeruginosa PAO1 has been determined at 2.54 Angstrom resolution. It is the first structure of a mem ber of homology family I.1 of bacterial lipases. The structure shows a vari ant of the alpha/beta hydrolase fold, with Ser(82), Asp(229), and His(251) as the catalytic triad residues. Compared with the "canonical" alpha/beta h ydrolase fold, the first two P-strands and one alpha-helix (alpha E) are no t present. The absence of helix alpha E allows the formation of a stabilizi ng intramolecular disulfide bridge. The loop containing His251 is stabilize d by an octahedrally coordinated calcium ion. On top of the active site a l id subdomain is in an open conformation, making the catalytic cleft accessi ble from the solvent region. A triacylglycerol analogue is covalently bound to Ser(82) in the active site, demonstrating the position of the oxyanion hole and of the three pockets that accommodate the sn-1, sn-2, and sn-3 fat ty acid chains. The inhibited enzyme can be thought to mimic the structure of the tetrahedral intermediate that occurs during the acylation step of th e reaction. Analysis of the binding mode of the inhibitor suggests that the size of the acyl pocket and the size and interactions of the sn-2 binding pocket are the predominant determinants of the regio- and enantio-preferenc e of the enzyme.