Title : The antithrombin P1 residue is important for target proteinase specificity but not for heparin activation of the serpin. Characterization of P1 antithrombin variants with altered proteinase specificity but normal heparin activation.

Pub. Date : 2001 Jun 5

PMID : 11380262






5 Functional Relationships(s)
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1 Heparin has been proposed to conformationally activate the serpin, antithrombin, by making the reactive center loop P1 arginine residue accessible to proteinases. Arginine serpin family C member 1 Homo sapiens
2 To evaluate this proposal, we determined the effect of mutating the P1 arginine on antithrombin"s specificity for target and nontarget proteinases in both native and heparin-activated states of the serpin. Arginine serpin family C member 1 Homo sapiens
3 As expected, mutation of the P1 arginine to tryptophan, histidine, leucine, and methionine converted the specificity of antithrombin from a trypsin inhibitor (k(assoc) = 2 x 10(5) M(-1) s(-1)) to a chymotrypsin inhibitor (k(assoc) = 10(3)-10(5) M(-1) s(-1)). Arginine serpin family C member 1 Homo sapiens
4 Mutation of the P1 arginine greatly reduced k(assoc) for antithrombin inhibition of thrombin and factor Xa from 40- to 5000-fold, but heparin normally accelerated the reactions of the variant antithrombins with these enzymes to make them reasonably efficient inhibitors (k(assoc) = 10(3)-10(4) M(-1) s(-1)). Arginine serpin family C member 1 Homo sapiens
5 Together, these findings suggest that the P1 arginine residue is similarly accessible to proteinases in both native and heparin-activated states of the serpin and contributes similarly to the specificity of antithrombin for thrombin and factor Xa in the two serpin conformational states. Arginine serpin family C member 1 Homo sapiens