Cloning, purification and characterisation of the lipase from Staphylococcus epidermidis -: Comparison of the substrate selectivity with those of other microbial lipases

On the chromosome of Staphylococcus epidermidis RP62A the lipase gene (gehSE1) is immediately flanked by the icaAA'BC operon, which is involved in biofilm formation. Since lipase production might play a role in staphylococcal skin colonisation as well, we studied the biochemical properties of the staphylococcal lipases more closely. The DNA sequence and the deduced protein sequence revealed that gehSE1 is very similar to the lipase sequence of S. epidermidis strain 9. Like other staphylococcal lipases, gehSE1 is organised as a preproenzyme. The part of gehSE1 coding for the mature lipase was cloned and overexpressed as a fusion protein with an N-terminal histidine tag in Escherichia coli. The lipase was purified to homogeneity using a combination of precipitation techniques, metal-affinity chromatography and gel filtration. Biochemical characterisation showed that this lipase is closely related to the lipase from Staphylococcus aureus NCTC8530. Both enzymes have a pH optimum around 6, are very stable at low pH, and need calcium as a cofactor for catalytic activity. The preferred substrates are small triacylglycerols, with a maximum activity toward tributyrylglycerol. Comparison of the substrate selectivity with those of other microbial lipases showed that phospholipids are generally poor substrates for lipases. An exception is the lipase from Staphylococcus hyicus, which prefers phospholipids as a substrate, distinguishing this staphylococcal lipase from other microbial lipases. These results are discussed in view of the structure/function relationships of staphylococcal lipases, and the possible involvement of these enzymes in biological processes such as skin colonisation and pathogenesis.