Abstract
It has been demonstrated that a unique pentasaccharide fragment of heparin (H5) activates AT by exposing an exosite on the serpin that is a recognition site for interaction with the basic autolysis loop (residues 143-154) of fXa. In support of this, the substitution of Arg-150 of fXa with Ala (R150A) impaired the reactivity of the mutant with AT by 1 order of magnitude specifically in the presence H5. To understand the mechanism by which heparin activation of AT improves the reactivity of the serpin with fXa, the H5-catalyzed reaction of AT with fXa, fXa R150A, and fXa S195A was studied using rapid kinetic, surface plasmon resonance, and competitive binding methods. The pseudo-first-order rate constants for the H5-catalyzed AT inhibition of both fXa and fXa R150A exhibited a linear dependence on the serpin concentration, thereby yielding second-order rate constants of 1.0 x 10(6) and 1.5 x 10(5) M(-)(1) s(-)(1), respectively. On the other hand, an approximately 70-saccharide, high-affinity heparin-catalyzed AT inhibition of both fXa derivatives showed a saturable dependence on the inhibitor concentration, yielding an identical rate constant of approximately 20 s(-)(1), but different ternary fXa-heparin-AT dissociation constants...Continue Reading
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Dec 7, 2007·Functional & Integrative Genomics·Thomas H Roberts, Jørn Hejgaard
Jul 16, 2010·The Journal of Biological Chemistry·Likui YangAlireza R Rezaie
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