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

EMBO J. 1997 Sep 1;16(17):5151-61. doi: 10.1093/emboj/16.17.5151.


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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Anticoagulants / chemistry*
  • Binding Sites
  • Computer Simulation
  • Crystallography, X-Ray
  • Factor Xa / chemistry*
  • Humans
  • Invertebrate Hormones / chemistry*
  • Leeches
  • Models, Molecular
  • Molecular Sequence Data
  • Protease Inhibitors / chemistry*
  • Protein Conformation
  • Recombinant Proteins / chemistry


  • Anticoagulants
  • Invertebrate Hormones
  • Protease Inhibitors
  • Recombinant Proteins
  • antistasin
  • hirustasin
  • Factor Xa

Associated data

  • PDB/1SKZ