Prothrombin requires two sequential metal-dependent conformational transitions to bind phospholipid. Conformation-specific antibodies directed against the phospholipid-binding site on prothrombin.

M Borowski; B C Furie; S Bauminger; B Furie

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PubMed · 2429962

Prothrombin requires two sequential metal-dependent conformational transitions to bind phospholipid. Conformation-specific antibodies directed against the phospholipid-binding site on prothrombin.

M Borowski·B C Furie·S Bauminger·B Furie

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Abstract

Prothrombin is a gamma-carboxyglutamic acid-containing protein that binds to phospholipid vesicles in the presence of calcium ions after undergoing a metal ion-induced conformational transition. To integrate recent data into a scheme that is compatible with our knowledge of prothrombin-metal interaction, we have proposed a new model of prothrombin structure. In this model prothrombin undergoes two metal-dependent conformational transitions: PT----PT'----PT*. The first transition is not cation-specific, but the second transition is metal-selective for Ca(II), Sr(II), or Ba(II). Only the PT* conformer binds to phospholipid surfaces. To test this model, anti-prothrombin antibodies that only bind to prothrombin in the presence of Ca(II) but not Mg(II) (PT*-specific) were isolated, and termed anti-prothrombin X Ca(II)-specific. Half-maximal binding of antibody to prothrombin was observed at 0.1 mM CaCl2 or 1 mM SrCl2, but no binding was observed with Mg(II), Mn(II), or Ba(II). However, prothrombin in the presence of both Mg(II)/Ba(II) or Mn(II)/Ba(II) demonstrated significant interaction with the antibody. Prothrombin binding to phospholipid vesicles was inhibited by the anti-prothrombin X Ca(II)-specific antibody or its Fab fragment, but was not inhibited by anti-prothrombin X Mg(II) antibody or its Fab fragment directed at the PT' conformer. These results support this three-state model for prothrombin. The metal specificity characteristic of prothrombin-phospholipid interaction is a property required for the expression of the phospholipid-binding site in the binary prothrombin-metal complex.

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Antibodies Antigen-Antibody Complex Binding Sites Epitopes Humans Kinetics Light Phospholipids Protein Binding Protein Conformation Prothrombin Radioimmunoassay Scattering, Radiation Journal Article Research Support, U.S. Gov't, P.H.S.

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M Borowski, B C Furie, S Bauminger, B Furie. 1986-11-15. Prothrombin requires two sequential metal-dependent conformational transitions to bind phospholipid. Conformation-specific antibodies directed against the phospholipid-binding site on prothrombin.. https://pubmed.ncbi.nlm.nih.gov/2429962/

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