Mutations which introduce free cysteine residues in the Gla-domain of vitamin K dependent proteins result in the formation of complexes with alpha 1-microglobulin.
We have previously described a genetic factor IX variant (Cys18-->Arg) for which we demonstrated that it had formed a heterodimer with alpha 1-microglobulin through formation of a disulphide bond with the remaining free cysteine residue of the disrupted disulphide bond in the Gla-domain of factor IX. Recently, we observed a similar high molecular weight complex for a genetic protein C variant (Arg-1-->Cys). Both the factor IX and the protein C variants have a defect in the calcium induced conformation. In this study we show that the aminoterminus of this protein C variant is prolonged with one amino acid, cysteine. This protein C variant, as well as protein C variants with Arg9-->Cys and Ser12-->Cys mutations which also carry a free cysteine residue, are shown to be present in plasma as a complex with alpha 1-microglobulin. A prothrombin variant with a Tyr44-->Cys mutation, had not formed such a complex. Furthermore, complexes between normal vitamin K-dependent clotting factors and alpha 1-microglobulin were shown to be present in plasma at low concentrations. The data suggest that the presence of an unpaired cysteine residue in the propeptide or the N-terminal half of the Gla-domain has strongly promoted the formation of a complex with alpha 1-microglobulin in the variants.
Wojcik
E G
EG
Haemostasis and Thrombosis Research Centre, University Hospital Leiden, Netherlands.
Simioni
P
P
d Berg
M
M
Girolami
A
A
Bertina
R M
RM
D000510:Alpha-Globulins / Q000737:chemistry*; D000595:Amino Acid Sequence; D001779:Blood Coagulation Factors / Q000737:chemistry / Q000235:genetics*; D003545:Cysteine / Q000737:chemistry*; D006801:Humans; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009154:Mutation; D015675:Osteocalcin / Q000737:chemistry / Q000235:genetics*; D014812:Vitamin K / Q000737:chemistry*
D000510:Alpha-Globulins; D001779:Blood Coagulation Factors; C016001:alpha-1-microglobulin; D015675:Osteocalcin; D014812:Vitamin K; D003545:Cysteine