| Description | This group of serine protease inhibitors belong to MEROPS inhibitor family I15, clan IO. They inhibit serine peptidases of the S1 family ( ) [ ] and are characterised by a well conserved pattern of cysteine residues. This is a family of leech anti-coagulants.Antistasin is a 15kDa protein found in the salivary glands of Haementeria officinalis (Mexican leech); it is an anticoagulant that functions by inhibiting factor Xa. The protein contains 119 residues, with an unusually high cysteine content (20 residues in all), and exhibits a 2-fold internal repeated structure. Four isoforms of antistasin have been identified in leech salivary gland extracts; partial sequence analysis indicates that these isoforms differ only by 1 or 2 amino acid residues [ ].Ghilanten is an anticoagulant-antimetastatic protein of Haementeria ghilianii (Amazon leech). Like antistasin, it contains 119 amino acids, with 20 cysteines, and a heparin-binding consensus motif at its C terminus. Arginine-34 is the residue involved in the active-site inhibition of trypsin and Factor Xa [ ].The 3D structure of antistasin has been determined to 1.9A resolution by X-ray crystallography [ ]. The structure reveals a novel protein fold comprising two similar domains, which can be divided into two similarly sized subdomains, with different relative orientations. Thus, the domain shapes differ, the N-terminal domain being wedge-shaped and the C-terminal domain flat []. Docking studies suggest that it is differences in domain shape that enable the N-terminal domain to bind and inhibit factor Xa, rather than the C-terminal domain, despite very similar active sites. A putative exosite binding region is evident in the N-terminal domain (residues 15-17), which is likely to interact with a cluster of positively charged residues on the factor Xa surface (Arg222/Lys223/Lys224), explaining the specificity and inhibitory potency of antistasin towards factor Xa. | Name | Proteinase inhibitor I15, leech antistasin |
| Short Name | Prot_inh_I15_antistasin_leech | Type | Family |
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