Lee S Y, Klevit R E
Department of Biochemistry, Biomolecular Structure Center, Box 357742, University of Washington, Seattle, Washington 98195-7742, USA.
Biochemistry. 2000 Apr 18;39(15):4225-30. doi: 10.1021/bi992697a.
Calmodulin is an essential Ca(2+)-binding protein involved in a multitude of cellular processes. The calmodulin sequence is highly conserved among all eukaryotic species; calmodulin from the yeast S. cerevisiae (yCaM) is the most divergent form, while still sharing 60% sequence identity with vertebrate calmodulin (vCaM). Although yCaM can be functionally substituted by vCaM in vivo, the two calmodulin proteins possess significantly different Ca(2+)-binding properties as well as abilities to activate vertebrate target enzymes in vitro. In addition, it has been observed that certain properties of the N-terminal and C-terminal domains of Ca(2+)-yCaM differ depending on whether they are in the context of the whole protein or isolated as half-molecule fragments. To investigate the structural basis for these differing properties, we have undertaken nuclear magnetic resonance (NMR) studies on yCaM and the two half-molecule fragments representing its two individual domains, yTr1(residues 1-76) and yTr2 (residues 75-146). We present direct evidence that the two domains of Ca(2+)-yCaM interact via their exposed hydrophobic surfaces. Thus, the Ca(2+)-bound form of yCaM exists in a novel compact structure in direct contrast to the well-established structure of Ca(2+)-vCaM comprised of two independent globular domains.
钙调蛋白是一种参与多种细胞过程的必需钙结合蛋白。钙调蛋白序列在所有真核生物物种中高度保守；来自酿酒酵母（yCaM）的钙调蛋白是最具差异的形式，但其与脊椎动物钙调蛋白（vCaM）仍有60%的序列同一性。尽管yCaM在体内可被vCaM功能替代，但这两种钙调蛋白在体外具有显著不同的钙结合特性以及激活脊椎动物靶酶的能力。此外，已经观察到Ca(2+)-yCaM的N端和C端结构域的某些特性因其处于整个蛋白质的背景下还是作为半分子片段分离而有所不同。为了研究这些不同特性的结构基础，我们对yCaM以及代表其两个独立结构域的两个半分子片段yTr1（第1 - 76位氨基酸残基）和yTr2（第75 - 146位氨基酸残基）进行了核磁共振（NMR）研究。我们提供了直接证据表明Ca(2+)-yCaM的两个结构域通过其暴露的疏水表面相互作用。因此，Ca(2+)-结合形式的yCaM以一种新颖的紧凑结构存在，这与由两个独立球状结构域组成的Ca(2+)-vCaM的既定结构形成直接对比。
