Blechner S L, Olah G A, Strynadka N C, Hodges R S, Trewhella J
Life Sciences Division, Los Alamos National Laboratory, New Mexico 87544.
Biochemistry. 1992 Nov 24;31(46):11326-34. doi: 10.1021/bi00161a010.
Small-angle X-ray scattering data have been measured for rabbit skeletal muscle troponin C and its complexes with the venom peptides melittin and mastoparan as well as synthetic peptides based on regions of the troponin I sequence implicated in troponin C binding. At the neutral pH used in this study (pH 6.8), troponin C shows a tendency to form dimers in the presence of 4 mol equiv of Ca2+, but is monomeric in solution when 2 or less mol equiv of Ca2+ is present. The 4Ca2+.troponin C dimers dissociate upon binding melittin, mastoparan, and peptides based on residues 96-115, 1-30, and 1-40 in the troponin I sequence. This result suggests that the peptide-binding sites overlap with the regions of contact between troponin C molecules forming a dimer. Like the structurally homologous calcium-binding protein calmodulin, troponin C shows conformational flexibility upon binding different peptides. Upon binding melittin, troponin C contracts in a similar manner to calmodulin when it binds peptides known to form amphiphilic helices (e.g., melittin, mastoparan, or MLCK-I). In contrast, mastoparan binding to troponin C does not result in a contracted structure. The scattering data indicate troponin C also remains in an extended structure upon binding the inhibitory peptides having the same sequence as residues 96-115 in troponin I.
已测量了兔骨骼肌肌钙蛋白C及其与蜂毒肽蜂毒明肽和mastoparan以及基于肌钙蛋白I序列中与肌钙蛋白C结合相关区域的合成肽形成的复合物的小角X射线散射数据。在本研究使用的中性pH值（pH 6.8）下，肌钙蛋白C在存在4摩尔当量Ca2+时显示出形成二聚体的倾向，但当存在2摩尔当量或更少的Ca2+时在溶液中为单体。4Ca2+·肌钙蛋白C二聚体在与蜂毒明肽、mastoparan以及基于肌钙蛋白I序列中96 - 115、1 - 30和1 - 40位残基的肽结合时会解离。该结果表明肽结合位点与形成二聚体的肌钙蛋白C分子之间的接触区域重叠。与结构同源的钙结合蛋白钙调蛋白一样，肌钙蛋白C在结合不同肽时表现出构象灵活性。在结合蜂毒明肽时，肌钙蛋白C与钙调蛋白结合已知形成两亲性螺旋的肽（如蜂毒明肽、mastoparan或肌球蛋白轻链激酶 - I）时的收缩方式相似。相比之下，mastoparan与肌钙蛋白C的结合不会导致收缩结构。散射数据表明，肌钙蛋白C在结合与肌钙蛋白I中96 - 115位残基具有相同序列的抑制性肽时也保持伸展结构。
