Identification of a Staphylococcal dipeptidase involved in the production of human body odour.

Abstract

The production of human body odour is the result of the action of commensal skin bacteria, including Staphylococcus hominis, acting to biotransform odourless apocrine gland secretions into volatile chemicals like thioalcohols such as 3-methyl-3-sulphanylhexan-1-ol (3M3SH). As the secreted odour precursor Cys-Gly-3M3SH contains a dipeptide, yet the final enzyme in the biotransformation pathway only functions on Cys-3M3SH, we sought to identify the remaining step in this human-adapted biochemical pathway using a novel coupled enzyme assay. Purification of this activity from S. hominis extracts led to the identification of the M20A-family PepV peptidase (ShPepV) as the primary Cys-Gly-3M3SH dipeptidase. To establish whether this was a primary substrate for PepV, the recombinant protein was purified and demonstrated broad activity against diverse dipeptides. The binding site for Cys-Gly-3M3SH was predicted using modelling, which suggested mutations that might accommodate this ligand more favourably. Indeed, a D437A resulted in an almost 6-fold increase in the k_cat/K_M, while other introduced mutations reduced or abolished function. Together these data identify an enzyme capable of catalysing the missing step in an ancient human-specific biochemical transformation and suggest that the production of 3M3SH neither uses a dedicated transporter nor peptidase for its breakdown, with only the final cleavage step, catalysed by PatB C-S β-lyase, being a unique enzyme.