Fighting an enemy within: cytoplasmic inhibitors of bacterial cysteine proteases

The genes encoding secreted, broad-spectrum activity cysteine proteases of Staphylococcus spp. (staphopains) and Streptococcus pyogenes (streptopain, SpeB) are genetically linked to genes encoding cytoplasmic inhibitors. While staphopain inhibitors have lipocalin-like folds, streptopain is inhibited by a protein bearing the scaffold of the enzyme profragment. Bioinformatic analysis of other prokaryotic genomes has revealed that two more species may utilize this same genetic arrangement to control streptopain-like proteases with lipocalin-like inhibitors, while three other species may employ a C-terminally located domain that resembles the profragment. This apparently represents a novel system that bacteria use to control the intracellular activity of their proteases.