Comparison of the Ca2+ binding properties of the gamma-carboxyglutamic acid-containing module of protein Z in the intact protein and in N-terminal fragments.
Protein Z is a vitamin K-dependent plasma protein of unknown function. Its modular structure is identical with those of factors VII, IX, X, and protein C. These proteins have an N-terminal gamma-carboxyglutamic acid (Gla)-containing module which binds six to ten Ca2+. In factors IX, X, and protein C, the adjacent epidermal growth factor (EGF)-like module binds one Ca2+ whereas the EGF-like module in protein Z does not. We have compared the Ca2+ binding properties of a fragment of protein Z comprising the Gla and N-terminal EGF-like modules (pZ-GlaEGFN) with those of intact protein Z and the isolated Gla module by measuring the Ca(2+)-induced quenching of the intrinsic protein fluorescence. The similar Ca2+ affinities of pZ-GlaEGFN and protein Z indicate that pZ-GlaEGFN has a native conformation and normal Ca2+ binding properties. A comparison of the Ca2+ binding to pZ-GlaEGFN with those to the corresponding fragments of factors IX, X, and protein C indicate that Ca2+ binding to the N-terminal EGF-like modules in the latter proteins does not influence the folding and Ca2+ binding properties of their Gla modules. Furthermore, the Ca(2+)-induced fluorescence enhancements of GlaEGF fragments from factors IX, X, and protein C appear to be caused by Ca2+ binding to the site in the EGF-like modules since it is not observed for pZ-GlaEGFN.
Persson
E
E
Department of Clinical Chemistry, University of Lund, Malmö General Hospital, Sweden.
Stenflo
J
J
D015055:1-Carboxyglutamic Acid; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001798:Blood Proteins / Q000378:metabolism*; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D002417:Cattle; D005164:Factor IX / Q000378:metabolism; D005170:Factor X / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism*; D011486:Protein C / Q000378:metabolism; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence
D000596:Amino Acids; D001798:Blood Proteins; D010446:Peptide Fragments; D011486:Protein C; C026080:plasma protein Z; D015055:1-Carboxyglutamic Acid; D005164:Factor IX; D005170:Factor X; D002118:Calcium