Domain

Pacifastin domain (IPR008037)

Short name: Pacifastin_dom

Domain relationships

None.

Description

Proteins containing this domain are proteinase inhibitors belonging to MEROPS inhibitor family I19 (clan IW) and sharing a pacifastin domain of ~35 residues, which contains a characteristic pattern of six conserved cysteine residues (C-x(9,12)-C-N-x-C-x-C-x(2,3)-G-x(3,6)-C-T-x(3)- C). The pacifastin domain consists of a twisted beta-sheet composed of three antiparallel strands and stabilised by an identical pattern (C1-C4, C2-C6, C3-C5) of disulfide bridges [PMID: 9192625, PMID: 11495915, PMID: 11997226, PMID: 11856311, PMID: 15631618, PMID: 19020355].

Proteins containing this domain were first isolated from Locusta migratoria migratoria(migratory locust). These were HI, LMCI-1 (PMP-D2) and LMCI-2 (PMP-C) [PMID: 1472051, PMID: 1740125, PMID: 10696590]; five additional members SGPI-1 to 5 were identified in Schistocerca gregaria (desert locust) [PMID: 9475173, PMID: 11856311], and a heterodimeric serine protease inhibitor (pacifastin) was isolated from the hemolymph of Pacifastacus leniusculus (Signal crayfish) [PMID: 9192625].

Pacifastin is a 155kDa composed of two covalently linked subunits, which are separately encoded. The heavy chain of pacifastin (105 kDa) is related to transferrins, containing three transferrin lobes, two of which seem to be active for iron binding [PMID: 9192625]. A number of the members of the transferrin family are also serine peptidases belong to MEROPS peptidase family S60 (IPR001156). The light chain of pacifastin (44 kDa) is the proteinase inhibitory subunit, and has nine cysteine-rich inhibitory domains that are homologous to each other. The locust inhibitors share a conserved array of six cysteine residues with the pacifastin light chain. The structure of members of this family reveal that they are comprised of a triple-stranded antiparallel beta-sheet connected by three disulphide bridges [PMID: 9192625].

The biological function(s) of the locust inhibitors is (are) not fully understood. LMCI-1 and LMCI-2 were shown to inhibit the endogenous proteolytic activating cascade of prophenoloxidase [PMID: 11997226]. Expression analysis shows that the genes encoding the SGPI precursors are differentially expressed in a time-, stage- and hormone-dependent manner.

GO terms

Biological Process

No terms assigned in this category.

Molecular Function

GO:0030414 peptidase inhibitor activity

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PROSITE profiles
SUPERFAMILY
Pfam