Conserved Site

Proteinase inhibitor I16, Streptomyces subtilisin-type inhibitor, conserved site (IPR020054)

Short name: Prot_inh_SSI_I16_CS


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, IPR000209) and are collectively known as Streptomyces subtilisin inhibitors (SSI). Some SSI also inhibit trypsin, chymotrypsin (MEROPS peptidase family S1, IPR001254) and griselysin (MEROPS peptidase family M4, IPR001570) [PMID: 14705960]. Mutation of the active site residue can influence inhibition specificity [PMID: 1908859].

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 which hydrophobic side-chains are sandwiched between 2 lobes [PMID: 6387152]. Loss of the C-terminal tetrapeptide VFAF 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 the correct 3D fold [PMID: 6993452]. 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 from a common ancestor [PMID: 6387152].

This entry represents a conserved site with two cysteines involved in a disulfide bond.

GO terms

Biological Process

No terms assigned in this category.

Molecular Function

GO:0004867 serine-type endopeptidase inhibitor activity

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PROSITE patterns