Human platelets contain forms of factor V in disulfide-linkage with multimerin

• Published in: Thrombosis and haemostasis Vol. 92; no. 6; p. 1349
• Main Authors: Hayward, Catherine P M, Fuller, Nola, Zheng, Shilun, Adam, Frédéric, Jeimy, Samira B, Horsewood, Ian, Quinn-Allen, Mary Ann, Kane, William H
• Format: Journal Article
• Language: English
• Published: Germany 01.12.2004
• Subjects: Blood Platelets - metabolism; Blood Proteins - chemistry; Blotting, Western; Cell Movement; Dimerization; Disulfides - chemistry; Electrophoresis, Gel, Two-Dimensional; Electrophoresis, Polyacrylamide Gel; Epitope Mapping; Epitopes - chemistry; Factor V - biosynthesis; Factor V - chemistry; Factor Va - metabolism; Glycoproteins - chemistry; Humans; Immunoprecipitation; Models, Biological; Polymers - chemistry; Protein Binding; Protein Structure, Tertiary; Secretory Vesicles - chemistry; Thrombin - chemistry; Thrombin - metabolism
• ISSN: 0340-6245
• DOI: 10.1160/TH03-02-0123

Factor V is an essential cofactor for blood coagulation that circulates in platelets and plasma. Unlike plasma factor V, platelet factor V is stored complexed with the polymeric alpha-granule protein multimerin. In analyses of human platelet factor V on nonreduced denaturing multimer gels, we identified that approximately 25% was variable in size and migrated larger than single chain factor V, the largest form in plasma. Upon reduction, the unusually large, variably-sized forms of platelet factor V liberated components that comigrated with other forms of platelet factor V, indicating that they contained factor V in interchain disulfide-linkages. With thrombin cleavage, factor Va heavy and light chain domains, but not B-domains,were liberated from the components linked by interchain disulfide bonds, indicating that the single cysteine in the B-domain at position 1085 was the site of disulfide linkage. Since unusually large factor V had a variable size and included forms larger than factor V dimers, the data suggested disulfide-linkage with another platelet protein, possibly multimerin. Immunoprecipitation experiments confirmed that unusually large factor V was associated with multimerin and it remained associated in 0.5 M salt. Moreover, platelets contained a subpopulation of multimerin polymers that resisted dissociation from factor V by denaturing detergent and comigrated with unusually large platelet factor V, before and after thrombin cleavage. The disulfide-linked complexes of multimerin and factor V in platelets, which are cleaved by thrombin to liberate factor Va, could be important for modulating the function of platelet factor V and its delivery onto activated platelets. Factor Va generation and function from unusually large platelet factor V is only speculative at this time.