Calcium binding to the epidermal growth factor homology region of bovine protein C.
A high affinity calcium binding site that is independent of the gamma-carboxyglutamic acid-rich amino-terminal region, has been demonstrated in bovine protein C, as well as in the other vitamin K-dependent proteins (except prothrombin) involved in blood coagulation. gamma-Carboxyglutamic acid-independent calcium binding in protein C is required for its rapid activation by the thrombin-thrombomodulin complex. We have now isolated a Ca2+-binding fragment from a tryptic digest of bovine protein C. The isolated fragment contains the two domains that are homologous to the epidermal growth factor precursor from the light chain of protein C, and a small disulfide bound peptide derived from the heavy chain. The isolated fragment bound 1 mol of Ca2+/mol of protein with a dissociation constant (Kd) of approximately 1 x 10(-4) M. This is similar to the Kd previously determined for binding of a single Ca2+ ion to protein C lacking the gamma-carboxyglutamic acid region. Immunochemical evidence indicated that Ca2+ binding induced a conformational change both in protein C lacking the gamma-carboxyglutamic acid region and in the isolated fragment.
Ohlin
A K
AK
Department of Clinical Chemistry, University of Lund, Malmö General Hospital, Sweden.
Linse
S
S
Stenflo
J
J
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D004815:Epidermal Growth Factor / Q000235:genetics / Q000378:metabolism*; D010446:Peptide Fragments / Q000032:analysis; D011485:Protein Binding; D011486:Protein C / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D014357:Trypsin
D010446:Peptide Fragments; D011486:Protein C; D004815:Epidermal Growth Factor; D014357:Trypsin; D002118:Calcium