The Gla domain of human prothrombin has a binding site for factor Va.
The role of the Gla domain of human prothrombin in interaction with the prothrombinase complex was studied using a peptide with the sequence of the first 46 residues of human prothrombin, PT-(1-46). Intrinsic fluorescence measurements showed that PT-(1-46) undergoes a conformational alteration upon binding calcium; this conclusion is supported by one-dimensional (1)H NMR spectroscopy, which identifies a change in the chemical environment of tryptophan 41. PT-(1-46) binds phospholipid membranes in a calcium-dependent manner with a K(d) of 0.5 microm and inhibits thrombin generation by the prothrombinase complex with a K(i) of 0.8 microm. In the absence of phospholipid membranes, PT-(1-46) inhibits thrombin generation by factor Xa in the presence but not absence of factor Va, suggesting that PT-(1-46) inhibits prothrombin-factor Va binding. The addition of factor Va to PT-(1-46) labeled with the fluorophore sulfosuccinimidyl-7-amino-4-methylcoumarin-3-acetic acid (PT-(1-46)AMCA) caused a concentration-dependent quenching of AMCA fluorescence, providing direct evidence of a PT-(1-46)-factor Va interaction. The K(d) for this interaction was 1.3 microm. These results indicate that the N-terminal Gla domain of human prothrombin is a functional unit that has a binding site for factor Va. The prothrombin Gla domain is important for interaction of the substrate with the prothrombinase complex.
Blostein
M D
MD
Center for Hemostasis and Thrombosis Research, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston Massachusetts 02215, USA.
Rigby
A C
AC
Jacobs
M
M
Furie
B
B
Furie
B C
BC
D000595:Amino Acid Sequence; D001665:Binding Sites; D004591:Electrophoresis, Polyacrylamide Gel; D015943:Factor Va / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D011516:Prothrombin / Q000737:chemistry / Q000378:metabolism*
D015943:Factor Va; D011516:Prothrombin