Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9573210 | Biophysical Chemistry | 2005 | 7 Pages |
Abstract
Thrombomodulin (TM) is as essential cofactor in protein C activation by thrombin. To investigate the cofactor effect of TM on the P3-P3â² binding specificity of thrombin, we prepared a Gla-domainless protein C (GDPC) and an antithrombin (AT) mutant in which the P3-P3â² residues of both molecules were replaced with the corresponding residues of the factor Xa cleavage site in prethrombin-2. TM is known to interact with GDPC, but not AT in the complex. Thrombin did not react with either mutant in the absence of a cofactor. While the thrombin-TM complex also did not react with the AT mutant, it activated the GDPC mutant with a normal kcat, but an â¼4-fold impaired Km value. Further studies revealed that the active-site directed inhibitor p-aminobenzamidine acts as a competitive inhibitor of both wild-type and GDPC mutant in reaction with the thrombin-TM complex. These results suggest that the interaction of the P3-P3â² residues of GDPC with the active-site pocket of the thrombin-TM complex makes a dominant contribution to the binding specificity of the reaction. Moreover, the observation that the GDPC mutant, but not the AT mutant, functions as an effective substrate for the thrombin-TM complex suggests that GDPC interaction with the thrombin-TM complex may be associated with the alteration of the conformation of the P3-P3â² residues of the substrate.
Related Topics
Physical Sciences and Engineering
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Physical and Theoretical Chemistry
Authors
Alireza R. Rezaie, Likui Yang,