The crystal structure of Bacillus subtilis lipase: A minimal alpha/beta hydrolase fold enzyme

The X-ray structure of the lipase LipA from Bacillus subtilis has been dete rmined at 1.5 Angstrom resolution. It is the first structure of a member of homology family 1.4 of bacterial lipases. The lipase shows a compact minim al alpha/beta hydrolase fold with a six-stranded parallel beta -sheet flank ed by five alpha -helices, two on one side of the sheet and three on the ot her side. The catalytic triad residues, Ser77, Asp133 and His156, and the r esidues forming the oxyanion hole (backbone amide groups of Ile12 and Met78 ) are in positions very similar to those of other lipases of known structur e. However, no lid domain is present and the active-site nucleophile Ser77 is solvent-exposed. A model of substrate binding is proposed on the basis o f a comparison with other lipases with a covalently bound tetrahedral inter mediate mimic. It explains the preference of the enzyme for substrates with C-8 fatty acid chains. (C) 2001 Academic Press.