Defining the factor Xa-binding site on factor Va by site-directed glycosylation.

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Activated Factor V (FVa) functions as a membrane-bound cofactor to the enzyme factor Xa (FXa) in the conversion of prothrombin to thrombin, increasing the catalytic efficiency of FXa by several orders of magnitude. To map regions on FVa that are important for binding of FXa, site-directed mutagenesis resulting in novel potential glycosylation sites on FV was used as strategy. The consensus sequence for N-linked glycosylation was introduced at sites, which according to a computer model of the A-domains of FVa, were located at the surface of FV. In total, thirteen different regions on the FVa surface were probed, including sites that are homologous to FIXa-binding sites on FVIII. The interaction between the FVa variants and FXa and prothrombin were studied in a functional prothrombin activation assay, as well as in a direct binding assay between FVa and FXa. In both assays, the four mutants carrying a carbohydrate side chain at position 467, 511, 652, or 1683, displayed attenuated FXa binding whereas the prothrombin affinity was unaffected. The affinity towards FXa could be restored when the mutants were expressed in the presence of tunicamycin to inhibit glycosylation, indicating the lost FXa affinity to be caused by the added carbohydrates. The results suggested regions surrounding residues 467, 511, 652, and 1683 in FVa to be important for FXa binding. This indicate the enzyme:cofactor assembly of the prothrombinase and the tenase complexes to be homologous and provides a useful platform for further investigation of specific structural elements involved in the FVa-FXa complex assembly.


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Medicinal Chemistry
Original languageEnglish
Pages (from-to)50022-50029
JournalJournal of Biological Chemistry
Issue number51
Publication statusPublished - 2002
Publication categoryResearch