The phospholipase activity of Staphylococcus hyicus lipase strongly depends on a single Ser to Val mutation

Site-directed mutagenesis and domain exchange were used to investigate the role of the C-terminal domains of Staphylococcus hyicus lipase (SHL) and S. aureus lipase (SAL) in substrate selectivity. The introduction of a single point mutation coding for the substitution of Val for Ser356 in SHL yields an enzyme which has retained full lipase activity, but with more than 12-fold lower phospholipase activity. Starting with this S356V variant of SHL the C-terminal 40 amino acids were replaced by the corresponding SAL sequence. Although 23 amino acid changes were introduced simultaneously the impact on the phospholipase/lipase activity ratio was only 4-fold. We therefore conclude that in the C-terminal domain it is Ser356 which mainly determines phospholipase activity. The introduction of a Val357 to Ser substitution in SAL did not turn SAL into a phospholipase, showing that residues from other domains contribute to this activity as well. The results are discussed in view of the sequence homology of lipases and (lyso)phospholipases.