CRYSTAL-STRUCTURE OF A BACTERIAL LIPASE FROM CHROMOBACTERIUM-VISCOSUMATCC-6918 REFINED AT 1.6 ANGSTROM RESOLUTION

The crystal structure of a lipase from the bacterium Chromobacterium v iscosum ATCC 6918 (CVL) has been determined by isomorphous replacement and refined at 1.6 Angstrom resolution to an X-factor of 17.8%. The l ipase has the overall topology of an alpha/beta type protein, which wa s also found for previously determined lipase structures. The catalyti c triad of the active center consists of the residues Ser87, Ap263 and His285. These residues are not exposed to the solvent, but a narrow c hannel connects them with the molecular surface. This conformation is very similar to the previously reported closed conformation of Pseudom onas glumae lipase (PGL), but superposition of the two lipase structur es reveals several conformational differences. r.m.s. deviations great er than 2 Angstrom are found for the C-proportional to-atoms of the po lypeptide chains from His15 to Asp28, from Leu49 to Ser54 and from Lys 128 to Gln158. Compared to the PGL structure in the CVL structure, thr ee alpha-helical fragments are shorter, one beta-strand is longer and an additional antiparallel beta-sheet is found. In contrast to PGL, CV L displays an oxyanion hole, which is stabilized by the amide nitrogen atoms of Leu17 and Gln88, and a cis-peptide bond between Gln291 and L eu292. CVL contains a Ca2+, like the PGL, which is coordinated by four oxygen atoms from the protein and two water molecules. (C) 1996 Acade mic Press Limited