Heidorn D B, Seeger P A, Rokop S E, Blumenthal D K, Means A R, Crespi H, Trewhella J
Life Sciences Division and Neutron Scattering Center, Los Alamos National Laboratory, New Mexico 87545.
Biochemistry. 1989 Aug 8;28(16):6757-64. doi: 10.1021/bi00442a032.
Small-angle X-ray and neutron scattering data were used to study the solution structure of calmodulin complexed with a synthetic peptide corresponding to residues 577-603 of rabbit skeletal muscle myosin light chain kinase. The X-ray data indicate that, in the presence of Ca2+, the calmodulin-peptide complex has a structure that is considerably more compact than uncomplexed calmodulin. The radius of gyration, Rg, for the complex is approximately 20% smaller than that of uncomplexed Ca2+.calmodulin (16 vs 21 A), and the maximum dimension, dmax, for the complex is also about 20% smaller (49 vs 67 A). The peptide-induced conformational rearrangement of calmodulin is [Ca2+] dependent. The length distribution function for the complex is more symmetric than that for uncomplexed Ca2+.calmodulin, indicating that more of the mass is distributed toward the center of mass for the complex, compared with the dumbell-shaped Ca2+.calmodulin. The solvent contrast dependence of Rg for neutron scattering indicates that the peptide is located more toward the center of the complex, while the calmodulin is located more peripherally, and that the centers of mass of the calmodulin and the peptide are not coincident. The scattering data support the hypothesis that the interconnecting helix region observed in the crystal structure for calmodulin is quite flexible in solution, allowing the two lobes of calmodulin to form close contacts on binding the peptide. This flexibility of the central helix may play a critical role in activating target enzymes such as myosin light chain kinase.
利用小角X射线和中子散射数据研究了与对应于兔骨骼肌肌球蛋白轻链激酶577 - 603位残基的合成肽复合的钙调蛋白的溶液结构。X射线数据表明，在Ca2+存在下，钙调蛋白 - 肽复合物的结构比未复合的钙调蛋白紧凑得多。复合物的回转半径Rg比未复合的Ca2+·钙调蛋白大约小20%（16 Å对21 Å），复合物的最大尺寸dmax也小约20%（49 Å对67 Å）。肽诱导的钙调蛋白构象重排是[Ca2+]依赖性的。复合物的长度分布函数比未复合的Ca2+·钙调蛋白更对称，这表明与哑铃状的Ca2+·钙调蛋白相比，复合物的更多质量分布在质心附近。中子散射中Rg对溶剂对比度的依赖性表明，肽更靠近复合物中心，而钙调蛋白更位于外围，并且钙调蛋白和肽的质心不重合。散射数据支持这样的假设：在钙调蛋白晶体结构中观察到的连接螺旋区域在溶液中相当灵活，使得钙调蛋白的两个叶在结合肽时能形成紧密接触。中心螺旋的这种灵活性可能在激活诸如肌球蛋白轻链激酶等靶酶中起关键作用。
