1.8-ANGSTROM REFINED STRUCTURE OF THE LIPASE FROM GEOTRICHUM-CANDIDUM

A lipase from the fungus Geotrichum candidum is one of only three interfacially activated lipases whose structures have been reported to date. We have previously reported the partially refined 2.2 Å structure of this enzyme. We have subsequently extended the resolution and here report the fully refined 1.8 Å structure of this lipase. The structure observed in the crystal is apparently not the lipolytic conformation, as the active site is not accessible from the surface of the molecule. A single large cavity is found in the interior of the molecule and extends from the catalytic Ser to two surface helices, suggesting that this face may be the region that interacts with the lipid interface. The mobility of local segments on this face is indicated by temperature factors larger than elsewhere in the molecule and by the observation of several residues whose side-chains are discretely disordered. These observations strongly suggest that this portion of the molecule is involved in interfacial and substrate binding, but the exact nature of the conformational changes induced by binding to the lipid interface can not be determined.