title: X-ray structure of antistasin at 1.9 A resolution and its modelled complex with blood coagulation factor Xa.
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.
authors.affiliation: Laboratory of Biophysical Chemistry and BIOSON Research Institute, Department of Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
authors.forename: R
authors.initials: R
authors.lastname: Lapatto
authors.forename: U
authors.initials: U
authors.lastname: Krengel
authors.forename: H A
authors.initials: HA
authors.lastname: Schreuder
authors.forename: A
authors.initials: A
authors.lastname: Arkema
authors.forename: B
authors.initials: B
authors.lastname: de Boer
authors.forename: K H
authors.initials: KH
authors.lastname: Kalk
authors.forename: W G
authors.initials: WG
authors.lastname: Hol
authors.forename: P D
authors.initials: PD
authors.lastname: Grootenhuis
authors.forename: J W
authors.initials: JW
authors.lastname: Mulders
authors.forename: R
authors.initials: R
authors.lastname: Dijkema
authors.forename: H J
authors.initials: HJ
authors.lastname: Theunissen
authors.forename: B W
authors.initials: BW
authors.lastname: Dijkstra
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000925:Anticoagulants / Q000737:chemistry*; D001665:Binding Sites; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D015951:Factor Xa / Q000737:chemistry*; D006801:Humans; D007447:Invertebrate Hormones / Q000737:chemistry*; D007865:Leeches; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011480:Protease Inhibitors / Q000737:chemistry*; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry
chemical_list: D000925:Anticoagulants; D007447:Invertebrate Hormones; D011480:Protease Inhibitors; D011994:Recombinant Proteins; C053155:antistasin; C086021:hirustasin; D015951:Factor Xa