title: Human platelets contain forms of factor V in disulfide-linkage with multimerin.
abstract: 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.
authors.affiliation: Department of Pathology, McMaster University, Hamilton, Ontario, Canada L8N 3Z5. haywrdc@mcmaster.ca
authors.forename: Catherine P M
authors.initials: CP
authors.lastname: Hayward
authors.forename: Nola
authors.initials: N
authors.lastname: Fuller
authors.forename: Shilun
authors.initials: S
authors.lastname: Zheng
authors.forename: Frédéric
authors.initials: F
authors.lastname: Adam
authors.forename: Samira B
authors.initials: SB
authors.lastname: Jeimy
authors.forename: Ian
authors.initials: I
authors.lastname: Horsewood
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Quinn-Allen
authors.forename: William H
authors.initials: WH
authors.lastname: Kane
mesh_terms: D001792:Blood Platelets / Q000378:metabolism*; D001798:Blood Proteins / Q000737:chemistry*; D015153:Blotting, Western; D002465:Cell Movement; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D018604:Epitope Mapping; D000939:Epitopes / Q000737:chemistry; D005165:Factor V / Q000096:biosynthesis* / Q000737:chemistry*; D015943:Factor Va / Q000378:metabolism; D006023:Glycoproteins / Q000737:chemistry; D006801:Humans; D047468:Immunoprecipitation; D008954:Models, Biological; D011108:Polymers / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D022142:Secretory Vesicles / Q000737:chemistry; D013917:Thrombin / Q000737:chemistry / Q000378:metabolism
chemical_list: D001798:Blood Proteins; D004220:Disulfides; D000939:Epitopes; D006023:Glycoproteins; D011108:Polymers; C069282:multimerin; D015943:Factor Va; D005165:Factor V; D013917:Thrombin