|Name||Inhibitor family I5 (ascidian family)|
|Family type peptidase||I05.001 - ascidian trypsin inhibitor (Halocynthia roretzi), MEROPS Accession MER0018234 (inhibitor unit: 1-55)|
|Content of family||Inhibitor family I5 contains a single inhibitor of serine peptidases.|
Identifier created: MEROPS 6.1 (10 January 2003)|
A trypsin inhibitor was discovered in the hemolymph of a solitary ascidian, Halocynthia roretzi (Yokosawa et al., 1985), and has been further characterised from that source, but no homologues from other organisms have been detected.
|Peptidases inhibited||Peptidases inhibited belong to family S1 and include mammalian trypsin (S01.151) and plasmin (S01.233) as well as the ascidian sperm peptidase acrosin (S01.223) (Kumazaki et al., 1994).|
|Mechanism of inhibition||The similarity in structure to the Kazal inhibitors suggests that ATI inhibits by the Laskowski mechanism.|
|Molecular structure||The solution structure of ATI was solved by Hemmi et al. (2002). It shows an alpha-helix (stabilized by cysteine interactions) and a three-stranded antiparallel beta-sheet. There are also four disulphide bridges that are thought to contribute to the stability of the reactive site loop (see the Alignment). The structure is similar to that of the Kazal-type inhibitors (family I1) and accordingly family I5 is placed in clan IA.|