Identification of essential aspartic acid and histidine residues of hormone-sensitive lipase: apparent residues of the catalytic triad.

It is expected that hormone-sensitive lipase (HSL), like most other lipases and esterases, adopts an alpha/beta-hydrolase fold and has a catalytic triad of serine, aspartic or glutamic acid, and histidine. Recently, we have published a three-dimensional model for the C-terminal catalytic domain of HSL, having an alpha/beta-hydrolase fold and with Ser-423(1), Asp-703 and His-733 in the catalytic triad (Contreras et al. (1996) J. Biol. Chem. 271, 31426-31430). It has been shown that Ser-423, situated in the motif GXSXG, is essential for catalysis (Holm et al. (1994) FEBS Lett. 344, 234-238). The suggested aspartic acid and histidine were here probed by site-directed mutagenesis. Mutants of residues Asp-703 and His-733 are devoid of both lipase and esterase activity, which is not the case for mutants of other tested aspartic acid and histidine residues. Thus, the presented data support the three-dimensional model structure with Asp-703 and His-733 as part of the traid.