The staphostatin family of cysteine protease inhibitors in the genus Staphylococcus as an example of parallel evolution of protease and inhibitor specificity.

Staphostatins constitute a family of staphylococcal cysteine protease inhibitors sharing a lipocalin-like fold and a unique mechanism of action. Each of these cytoplasmic proteins is co-expressed from one operon, together with a corresponding target extracellular cysteine protease (staphopain). To cast more light on staphostatin/staphopain interaction and the evolution of the encoding operons, we have cloned and characterized a staphopain (StpA2 _{aur CH-91}) and its inhibitor (StpinA2 _{aur CH-91}) from a novel staphylococcal thiol protease operon ( stpAB2 _CH-91) identified in S. aureus strain CH-91. Furthermore, we have expressed a staphostatin from Staphylococcus warneri (StpinB _war) and characterized its target protease (StpB_war). Analysis of the reciprocal interactions among novel and previously described members of the staphostatin and staphopain families demonstrates that the co-transcribed protease is the primary target for each staphostatin. Nevertheless, the inhibitor derived from one species of Staphylococcus can inhibit the staphopain from another species, although the K_i values are generally higher and inhibition only occurs if both proteins belong to the same subgroup of either S. aureus staphopain A/staphostatin A (α group) or staphopain B/staphostatin B (β group) orthologs. This indicates that both subgroups arose in a single event of ancestral allelic duplication, followed by parallel evolution of the protease/inhibitor pairs. The tight coevolution is likely the result of the known deleterious effects of uncontrolled staphopain action. [ABSTRACT FROM AUTHOR]