Calcium-dependent interaction between the epidermal growth factor precursor-like region of human protein C and a monoclonal antibody.
Protein C, like the other vitamin K-dependent plasma proteins that participate in blood coagulation, except prothrombin, has at least one high affinity calcium-binding site that is independent of gamma-carboxyglutamic acid. Calcium binding to this site is required for activation of protein C by the thrombin-thrombomodulin complex. In an attempt to localize this calcium-binding site, we subjected protein C to limited tryptic digestion. A monoclonal antibody that recognizes a calcium-dependent epitope both in intact protein C, in gamma-carboxyglutamic acid-domainless protein C, and in activated protein C, was used to isolate a fragment from the tryptic digest. The fragment was derived from the light chain of protein C and consisted of the two domains that are homologous to the epidermal growth factor precursor. Half-maximal binding of the intact protein and of the isolated fragment by the antibody occurred at 100-200 microM Ca2+. The results suggest the presence of a Ca2+-binding site in the epidermal growth factor homology region of protein C.
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000911:Antibodies, Monoclonal; D002118:Calcium / Q000378:metabolism*; D004815:Epidermal Growth Factor / Q000276:immunology / Q000378:metabolism*; D000939:Epitopes / Q000276:immunology*; D006801:Humans; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D011486:Protein C / Q000276:immunology / Q000378:metabolism*; D011487:Protein Conformation; D011498:Protein Precursors / Q000276:immunology / Q000378:metabolism*; D014357:Trypsin / Q000378:metabolism
D000596:Amino Acids; D000911:Antibodies, Monoclonal; D000939:Epitopes; D010446:Peptide Fragments; D011486:Protein C; D011498:Protein Precursors; D004815:Epidermal Growth Factor; D014357:Trypsin; D002118:Calcium