Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10765576 | Biochemical and Biophysical Research Communications | 2009 | 6 Pages |
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-P3â² 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-P3â² positions of the reactive center loop. Inhibition kinetic studies indicated that the reactivity of P2-Phe with fXa was significantly (â¼5-fold) impaired, however, the P3-P3â² mutant exhibited 1.5-fold improved reactivity with the protease, suggesting cooperative effects between P3-P3â² 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-P3â² 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.
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Authors
Likui Yang, Shabir H. Qureshi, Chandrashekhara Manithody, Alireza R. Rezaie,