American Society of Hirudotherapy

X-ray structure of antistasin at 1.9 A resolution and its modelled complex with blood coagulation factor Xa

Research article published in EMBO Journal (1997)

Last Updated: June 18, 2026Reviewed by: ASH Editorial Board
Research article — evidence reviewArticle reference
Evidence: Observational studyDrug DevelopmentLapatto R et al. · EMBO Journal, 1997

Abstract

The three-dimensional structure of antistasin, a potent inhibitor of blood coagulation factor Xa, from the Mexican leech Haementeria officinalis was determined at 1.9 A resolution by X-ray crystallography. The structure reveals a novel protein fold composed of two homologous domains, each resembling the structure of hirustasin, a related 55-residue protease inhibitor. However, hirustasin has a different overall shape than the individual antistasin domains, it contains four rather than two beta-strands, and does not inhibit factor Xa. The two antistasin domains can be subdivided into two similarly sized subdomains with different relative orientations. Consequently, the domain shapes are different, the N-terminal domain being wedge-shaped and the C-terminal domain flat. Docking studies suggest that differences in domain shape enable the N-terminal, but not C-terminal, domain of antistasin to bind and inhibit factor Xa, even though both have a very similar reactive site. Furthermore, a putative exosite binding region could be defined in the N-terminal domain of antistasin, comprising residues 15-17, which is likely to interact with a cluster of positively charged residues on the factor Xa surface (Arg222/Lys223/Lys224). This exosite binding region explains the specificity and inhibitory potency of antistasin towards factor Xa. In the C-terminal domain of antistasin, these exosite interactions are prevented due to the different overall shape of this domain.

Abstract sourced from PubMed (NCBI) for the cited record. See the original publication for the authoritative version.

Publication typeComparative StudyJournal ArticleResearch Support, Non-U.S. Gov't
Indexed MeSH termsAmino Acid SequenceAnimalsAnticoagulantsBinding SitesComputer SimulationCrystallography, X-RayFactor XaHumansInvertebrate HormonesLeechesModels, MolecularMolecular Sequence Data

Summary

X-ray structure of antistasin at 1.9 A resolution and its modelled complex with blood coagulation factor Xa.

Why This Matters for Hirudotherapy

This study determined the 1.9 Å X-ray crystal structure of antistasin, a potent factor Xa inhibitor from the Mexican leech Haementeria officinalis, and modeled its complex with factor Xa. The structure reveals two homologous domains; docking studies suggest the N-terminal domain (wedge-shaped) can bind and inhibit factor Xa via a defined exosite region, while the flat C-terminal domain cannot despite a similar reactive site. This is relevant to ASH as a leech-derived anticoagulant structure-function study. Caveat: the findings are structural/computational (modeled complex) with no in vivo or clinical validation.

Citation

X-ray structure of antistasin at 1.9 A resolution and its modelled complex with blood coagulation factor Xa

Lapatto R et al. · EMBO Journal, 1997

DOI

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