Immunochemical studies of conformational alterations in bone gamma-carboxyglutamic acid containing protein.
The Ca2+-dependent transition of the vitamin K dependent bone protein bone Gla-containing protein (BGP) was investigated by use of anti-BGP antibody that reacts with the Ca2+-dependent conformation of BGP. Antibody binding occurred in the presence of Ca2+ or Mg2+ with a Kd(app) of 1.75 mM for Ca2+. Upon removal of Ca2+ with ethylenediaminetetraacetic acid, antibody binding was eliminated. Upon thermal acid decarboxylation of BGP, Ca2+-independent binding of the antibody was restored. Thus, the epitope not expressed by fully carboxylated BGP in the absence of calcium ion was restored either by addition of Ca2+ or by decarboxylation of the protein. Circular dichroic studies of fully carboxylated and fully decarboxylated BGP indicated that addition of Ca2+ to the fully carboxylated protein or decarboxylation to produce the glutamic acid containing equivalent of BGP resulted in increased order structure (apparent alpha-helix) in the protein, and this alteration was coincident with antibody binding. These data suggest that carboxylation of this vitamin K dependent protein may lead to increased disorder in the protein as compared to the glutamic acid containing equivalent. Upon Ca2+ binding a structure more equivalent to the Glu-containing protein is obtained.
D000818:Animals; D000906:Antibodies; D000936:Antigen-Antibody Complex; D001842:Bone and Bones / Q000032:analysis*; D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000302:isolation & purification; D002417:Cattle; D002942:Circular Dichroism; D007106:Immune Sera; D008274:Magnesium / Q000494:pharmacology; D015675:Osteocalcin; D011485:Protein Binding; D011487:Protein Conformation
D000906:Antibodies; D000936:Antigen-Antibody Complex; D002135:Calcium-Binding Proteins; D007106:Immune Sera; D015675:Osteocalcin; D008274:Magnesium; D002118:Calcium