Persson E, Stenflo J
Department of Clinical Chemistry, University of Lund, Malmö General Hospital, Sweden.
FEBS Lett. 1992 Dec 7;314(1):5-9. doi: 10.1016/0014-5793(92)81447-t.
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.
蛋白Z是一种功能未知的维生素K依赖血浆蛋白。其模块化结构与因子VII、IX、X及蛋白C的结构相同。这些蛋白具有一个含N端γ-羧基谷氨酸（Gla）的模块，该模块可结合6至10个Ca2+。在因子IX、X及蛋白C中，相邻的表皮生长因子（EGF）样模块结合1个Ca2+，而蛋白Z中的EGF样模块则不结合。我们通过测量Ca(2+)诱导的蛋白质固有荧光淬灭，比较了包含Gla和N端EGF样模块的蛋白Z片段（pZ-GlaEGFN）与完整蛋白Z及分离的Gla模块的Ca2+结合特性。pZ-GlaEGFN与蛋白Z相似的Ca2+亲和力表明pZ-GlaEGFN具有天然构象和正常的Ca2+结合特性。将pZ-GlaEGFN的Ca2+结合情况与因子IX、X及蛋白C相应片段的Ca2+结合情况进行比较，结果表明Ca2+与后几种蛋白中N端EGF样模块的结合并不影响其Gla模块的折叠和Ca2+结合特性。此外，因子IX、X及蛋白C的GlaEGF片段的Ca(2+)诱导荧光增强似乎是由Ca2+与EGF样模块中的位点结合所致，因为在pZ-GlaEGFN中未观察到这种情况。
