Coagulin (IPR000275)

Short name: Coagulin

Overlapping homologous superfamilies

Family relationships



Coagulogen is a gel-forming protein of hemolymph that hinders the spread of invaders by immobilising them [PMID: 3905780, PMID: 6469947]. The protein contains a single 175- residue polypeptide chain; this is cleaved after Arg-18 and Arg-46 by a clotting enzyme contained in the hemocyte and activated by a bacterial endotoxin (lipopolysaccharide). Cleavage releases two chains of coagulin, A and B, linked by two disulphide bonds, together with the peptide C [PMID: 3905780, PMID: 6469947]. Gel formation results from interlinking of coagulin molecules. Secondary structure prediction suggests the C peptide forms an alpha- helix, which is released during the proteolytic conversion of coagulogen to coagulin gel [PMID: 3905780]. The beta-sheet structure and 16 half-cystines found in the molecule appear to yield a compact protein stable to acid and heat.

Mammalian blood coagulation is based on the proteolytically induced polymerisation of fibrinogens. Initially, fibrin monomers noncovalently interact with each other. The resulting homopolymers are further stabilised when the plasma transglutaminase (TGase) intermolecularly cross-links epsilon-(gamma-glutamyl)lysine bonds. In crustaceans, hemolymph coagulation depends on the TGase-mediated cross-linking of specific plasma-clotting proteins, but without the proteolytic cascade. In horseshoe crabs, the proteolytic coagulation cascade triggered by lipopolysaccharides and beta-1,3-glucans leads to the conversion of coagulogen into coagulin, resulting in noncovalent coagulin homopolymers through head-to-tail interaction. Horseshoe crab TGase, however, does not cross-link coagulins intermolecularly. Recently, we found that coagulins are cross-linked on hemocyte cell surface proteins called proxins. This indicates that a cross-linking reaction at the final stage of hemolymph coagulation is an important innate immune system of horseshoe crabs [PMID: 15170505].

GO terms

Biological Process

GO:0042381 hemolymph coagulation

Molecular Function

No terms assigned in this category.

Cellular Component

GO:0005576 extracellular region

Contributing signatures

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