SEQUENCE, CRYSTAL-STRUCTURE DETERMINATION AND REFINEMENT OF 2 CRYSTALFORMS OF LIPASE-B FROM CANDIDA-ANTARCTICA

Background: Lipases constitute a family of enzymes that hydrolyze trig lycerides. They occur in many organisms and display a wide variety of substrate specificities. In recent years, much progress has been made towards explaining the mechanism of these enzymes and their ability to hydrolyze their substrates at an oil-water interface. Results: We hav e determined the DNA and amino acid sequences for lipase B from the ye ast Candida antarctica. The primary sequence has no significant homolo gy to any other known lipase and deviates from the consensus sequence around the active site serine that is found in other lipases. We have determined the crystal structure of this enzyme using multiple isomorp hous replacement methods for two crystal forms. Models for the orthorh ombic and monoclinic crystal forms of the enzyme have been refined to 1.55 Angstrom and 2.1 Angstrom, resolution, respectively. Lipase B is an alpha/beta type protein that has many features in common with previ ously determined lipase structures and other related enzymes. In the m onoclinic crystal form, lipid-like molecules, most likely beta-octyl g lucoside, can be seen close to the active site. The behaviour of these lipid molecules in the crystal structure has been studied at differen t pH values. Conclusion: The structure of Candida antarctica lipase B shows that the enzyme has a Ser-His-Asp catalytic triad in its active site. The structure appears to be in an 'open' conformation with a rat her restricted entrance to the active site. We believe that this accou nts for the substrate specificity and high degree of stereospecificity of this lipase.