Shaw G S, Hodges R S, Sykes B D
Department of Biochemistry, University of Alberta, Edmonton, Canada.
Science. 1990 Jul 20;249(4966):280-3. doi: 10.1126/science.2374927.
The 70-residue carboxyl-terminal domain of the muscle contractile protein troponin-C contains two helix-loop-helix calcium (Ca)-binding sites that are related to each other by approximate twofold rotational symmetry. Hydrophobic residues from the helices and a short three residue beta sheet at the interface of the two sites act to stabilize the protein domain in the presence of Ca. A synthetic 34-residue peptide representing one of these sites (site III) has been synthesized and studied by H-1 nuclear magnetic resonance (NMR) spectroscopy. In solution this peptide undergoes a Ca-induced conformational change to form the helix-loop-helix Ca-binding motif. Two-dimensional nuclear Overhauser effect spectra have provided evidence for the formation of a beta sheet and interactions between several hydrophobic residues from opposing helices as found in troponin-C. It is proposed that a symmetric two-site dimer similar in tertiary structure to the carboxyl-terminal domain of troponin-C forms from the assembly of two site III peptides in the Ca-bound form.
肌肉收缩蛋白肌钙蛋白C的70个残基羧基末端结构域包含两个螺旋-环-螺旋钙（Ca）结合位点，这两个位点通过近似二重旋转对称相互关联。来自螺旋的疏水残基以及两个位点界面处的一个短的三残基β折叠在有Ca存在时起到稳定蛋白质结构域的作用。一种代表其中一个位点（位点III）的34个残基的合成肽已被合成，并通过H-1核磁共振（NMR）光谱进行了研究。在溶液中，这种肽会发生Ca诱导的构象变化，形成螺旋-环-螺旋Ca结合基序。二维核Overhauser效应光谱为β折叠的形成以及肌钙蛋白C中发现的来自相对螺旋的几个疏水残基之间的相互作用提供了证据。有人提出，由两个以Ca结合形式存在的位点III肽组装形成的对称双位点二聚体，其三级结构与肌钙蛋白C的羧基末端结构域相似。
