Family I9
Summary for family I9
| Name | Inhibitor family I9 (YIB family) |
|---|
| Family type peptidase | I09.003 - peptidase B inhibitor (fungus) (Saccharomyces cerevisiae), MEROPS Accession MER0018320 (inhibitor unit: 2-75) |
| Content of family | Inhibitor family I9 contains inhibitors of serine peptidases of the subtilisin family (S8). |
| History |
Identifier created: MEROPS 6.1 (10 January 2003)
Family I9 includes inhibitors such as the proteinase B inhibitor from Saccharomyces cerevisiae (I09.003), that are gene products in their own right, as well as the activation peptides from peptidases of the subtilisin family (S8), which are fragments released from the peptidase precursors. The subtilisin propeptides are known to function as molecular chaperones, assisting in the folding of the mature peptidase (Li et al., 1995), but have also been shown to act as 'temporary inhibitors' (Kojima et al., 1997; see below). |
| Peptidases inhibited | Peptidases inhibited belong to family S8 (Kojima et al., 1999). The proteinase B inhibitor inhibits cerevisin (S08.052, formerly known as proteinase B). The propeptide from subtilisin BPN" (I09.001) is initially a potent inhibitor of its parent peptidase following release, but potency is reduced following cleavage by the bound subtilisin, hence it has been described as a 'temporary inhibitor' (Kojima et al., 1997). |
| Mechanism of inhibition | Cerevisin is optimally active at pH 5, and gradual activation of the peptidase precursor at that pH was initially explained by degradation of the proteinase B inhibitor by saccharopepsin (A01.018) or carboxypeptidase Y (S10.001) (Lenney 1975); however, gradual activation still occurred in preparations lacking saccharopepsin and the alternative explanation was put forward that different forms of the inhibitor exist with differing stability at pH 5 (Magni et al., 1986). |
| Molecular structure | The proteinase B inhibitor consists of 74 residues and unusually for an inhibitor does not contain cysteine residues (Maier et al., 1979). Two isoforms of the inhibitor exist with minor differences in structure and inhibitory properties (Maier et al., 1979). The tertiary structure of the propeptide in complex with subtilisin BPN" has been determined (Gallagher et al., 1995), and shows an alpha/beta protein with a fold unlike that of any other protein. Hence family I9 is the only family in clan JC. |
| Clan | JC |
| Inhibitors and Homologues |
MEROPS ID |
Structure |
| subtilisin propeptide | I09.001 | Yes |
| peptidase A inhibitor 1 (Pleurotus ostreatus) | I09.002 | Yes |
| peptidase B inhibitor (fungus) | I09.003 | - |
| subtilisin propeptide-like inhibitor 1 (Arabidopsis thaliana) | I09.004 | - |
| Family I09 non-peptidase homologues | non-peptidase homologue | - |
| Family I09 unassigned peptidases | unassigned | - |
