| Type: | Domain | Name: | Subtilisin inhibitor |
| Description: | The Streptomyces family of bacteria produce a number of proteinase inhibitors, which belong to MEROPS inhibitor family I16, clan IY. They are characterised by their strong activity towards subtilisin (MEROPS peptidase family S8, ) and are collectively known as Streptomyces subtilisin inhibitors (SSI). Some SSI also inhibit trypsin, chymotrypsin (MEROPS peptidase family S1, ) and griselysin (MEROPS peptidase family M4, ) []. Mutation of the active site residue can influenceinhibition specificity [].SSI is a homodimer, each monomer containing 2 anti-parallel beta-sheets and 2 short alpha-helices. Protease binding induces the widening of a channel-like structure, in whichhydrophobic side-chains are sandwiched between 2 lobes []. Loss of the C-terminal tetrapeptideVFAF drastically reduces the inhibitory effect of the proteins when there is less than one molecule of inhibitor present per molecule of enzyme. This implies that the tetrapeptide is neccessary to maintain thecorrect 3D fold []. Structural similarities between the primary and secondary contact loops of SSI,and the ovomucoid and pancreatic secretory trypsin inhibitor family suggest evolution of the 2 families froma common ancestor []. | Short Name: | Subtilisin_inhibitor |
