title: Role of P2 glycine in determining the specificity of antithrombin reaction with coagulation proteases.
abstract: Structural data suggests that bulky hydrophobic residues at the S2-S4 sub-sites of factor Xa (fXa) restrict the preference of this pocket for small and non-polar residues like Gly at the P2 position of substrates and inhibitors. However, kinetic studies monitoring the cleavage specificity of 10-residue peptides by fXa have identified Phe as the most preferred P2 residue and Gln-Phe-Arg-Ser-Leu-Ser as the most preferred P3-P3' residues for recognition by fXa. To determine whether this mechanism of specificity is also true for fXa reaction with antithrombin (AT), we prepared two AT mutants having either a Phe at the P2 or Gln-Phe-Arg-Ser-Leu-Ser at the P3-P3' positions of the reactive center loop. Inhibition kinetic studies indicated that the reactivity of P2-Phe with fXa was significantly (approximately 5-fold) impaired, however, the P3-P3' mutant exhibited 1.5-fold improved reactivity with the protease, suggesting cooperative effects between P3-P3' residues influence the P2 specificity of AT. Substitution of Tyr-99 of fXa with a Gly dramatically impaired the reactivity of fXa with wild-type AT, but improved its reactivity with the serpin mutants in the absence, but not in the presence of pentasaccharide. AT with a P2-Phe inhibited thrombin with >150-fold impaired reactivity, however, the defect was restored by either pentasaccharide or by replacing Leu-99 of thrombin with a Gly. The P3-P3' mutant rapidly inhibited factors VIIa and XIa independent of pentasaccharide. These results indicate that P2-Gly plays a key role in determining the S2 sub-site specificity and target protease selectivity of AT in circulation.
authors.affiliation: Department of Biochemistry and Molecular Biology, St. Louis University School of Medicine, St. Louis, MO 63104, USA.
authors.forename: Likui
authors.initials: L
authors.lastname: Yang
authors.forename: Shabir H
authors.initials: SH
authors.lastname: Qureshi
authors.forename: Chandrashekhara
authors.initials: C
authors.lastname: Manithody
authors.forename: Alireza R
authors.initials: AR
authors.lastname: Rezaie
mesh_terms: D000595:Amino Acid Sequence; D000990:Antithrombin III / Q000235:genetics / Q000378:metabolism*; D001777:Blood Coagulation; D002460:Cell Line; D015942:Factor VIIa / Q000378:metabolism*; D015951:Factor Xa / Q000378:metabolism*; D005998:Glycine / Q000235:genetics / Q000378:metabolism*; D006801:Humans
chemical_list: D000990:Antithrombin III; D015942:Factor VIIa; D015951:Factor Xa; D005998:Glycine