Family I5


Summary Holotypes Alignment Genomes Structure Literature

Summary for family I5

NameInhibitor family I5 (ascidian family)
Family type peptidaseI05.001 - ascidian trypsin inhibitor (Halocynthia roretzi), MEROPS Accession MER0018234 (inhibitor unit: 1-55)
Content of familyInhibitor family I5 contains a single inhibitor of serine peptidases.
History 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 inhibitedPeptidases 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 inhibitionThe similarity in structure to the Kazal inhibitors suggests that ATI inhibits by the Laskowski mechanism.
Molecular structureThe 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.
Distribution of family Bacteria -  
Archaea -  
Protozoa -  
Fungi -  
Plants -  
Animals details  
Viruses -  
Biological functionsIt ATI is thought to have a role in the defence mechanism, inhibiting trypsin-like peptidases that are released from haemocytes upon phagocytosis (Yokosawa et al., 1985).
Statistics for family I5Sequences:2
Identifiers with PDB entries:1
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Other databases CATH
SCOP 57468
Inhibitors and Homologues MEROPS ID Structure
ascidian trypsin inhibitorI05.001Yes
family I5 unassigned peptidase inhibitor homologueshomologue-
family I5 unassigned peptidase inhibitorsunassigned-