text: Heparin-binding exosite of factor Xa.
  Recent studies have indicated that the basic residues Arg(93), Lys(96), Arg(125), Arg(165), Lys(169), Lys(236), and Arg(240) (chymotrypsin numbering) constitute an exosite in the catalytic domain of factor Xa that can effectively bind heparin only if the acidic N-terminal Gla domain of the proteinase was neutralized by physiological levels of calcium. Binding of a full-length heparin chain to this site of factor Xa in the presence of calcium makes a significant contribution to acceleration of the proteinase inhibition by antithrombin through a ternary complex bridging or template mechanism. Moreover, certain basic residues of this site, particularly Arg(165) and Lys(169), play a key role in factor Va and/or prothrombin recognition by factor Xa in the prothrombinase complex. This article reviews recent structural, mutagenesis and kinetic data that lead to identification of this exosite and discusses how the binding of protein or polysaccharide cofactors to this site of factor Xa can modulate the specificity and physiological function of this key coagulant enzyme in plasma.
entities.id: T10 T11 T12 T13 T14 T15 T16 T17 T18 T19 T1 T20 T21 T22 T23 T24 T2 T3 T4 T5 T6 T7 T8 T9
entities.type: CHEMICAL CHEMICAL CHEMICAL GENE-N GENE-Y GENE-N GENE-N GENE-Y GENE-N GENE-Y CHEMICAL GENE-Y GENE-Y GENE-Y GENE-Y GENE-Y CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL
entities.text: Arg Arg Lys chymotrypsin factor Xa N-terminal Gla domain proteinase factor Xa proteinase antithrombin Lys factor Va prothrombin factor Xa factor Xa factor Xa Arg N calcium calcium Arg Lys Arg Lys