Blood coagulation requires the conversion of zymogens to active enzymes. These reactions are facilitated by Ca2+-dependent protein binding to membrane surfaces containing anionic phospholipids. Here it is shown that only in the presence of both Ca2+ and phospholipid vesicles composed of phosphatidylcholine and phosphatidylserine can a prothrombin dimer be chemically cross-linked. A cross-linker containing evenly spaced reactive groups was prepared by activating the carboxy groups of a ten-residue glutamic acid peptide and allowed to react with physiological concentrations of prothrombin. When Ca2+ and anionic phospholipids were both present during exposure to the cross-linker, it was found that more than 50% of the prothrombin was trapped as a chemically defined dimer with reaction times of the order of 1 min. The dimer yield remained high even when reactions were performed at high phospholipid-to-protein ratios at protein concentrations an order of magnitude less than physiological. Amino acid sequencing of a CNBr peptide produced from the purified dimer localized the cross-link to residues Lys341 and Lys427 of prothrombin. The specificity and high yield under mild conditions of the cross-linking suggest that dimeric membrane bound prothrombin might be a physiologically relevant substrate for the formation of thrombin. Prothrombinase converts this modified protein to an enzyme that catalyses the hydrolysis of a thrombin chromogenic substrate as efficiently as thrombin and is inhibited by a thrombin active-site directed inhibitor, but is a thrombin dimer. The thrombin dimer has impaired activity compared with thrombin with respect to physiological functions requiring binding to exosite I. A model based on the known structure of thrombin is presented that can account for the prothrombin dimer and the properties of the dimeric thrombin formed from it.
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December 1998
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Research Article|
December 15 1998
A dimeric form of prothrombin on membrane surfaces
Peter J. ANDERSON
Peter J. ANDERSON
1
1Department of Biochemistry, University of Ottawa, 451 Smyth Road, Ottawa, Ontario, Canada K1H 8M5
1E-mail [email protected].
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Publisher: Portland Press Ltd
Received:
July 09 1998
Revision Received:
September 10 1998
Accepted:
October 07 1998
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London © 1998
1998
Biochem J (1998) 336 (3): 631–638.
Article history
Received:
July 09 1998
Revision Received:
September 10 1998
Accepted:
October 07 1998
Citation
Peter J. ANDERSON; A dimeric form of prothrombin on membrane surfaces. Biochem J 15 December 1998; 336 (3): 631–638. doi: https://doi.org/10.1042/bj3360631
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