SPring-8, Japan Synchrotron Radiation Research Institute, Kouto, Sayo, Hyogo 679-5198, Japan.
Biochemistry. 2012 May 15;51(19):3963-70. doi: 10.1021/bi3002192. Epub 2012 May 1.
Calmodulin undergoes characteristic conformational changes by binding Ca(2+), which allows it to bind to more than 300 target proteins and regulate numerous intracellular processes in all eukaryotic cells. We measured the conformational changes of calmodulin upon Ca(2+) and mastoparan binding using the time-resolved small-angle X-ray scattering technique combined with flash photolysis of caged calcium. This measurement system covers the time range of 0.5-180 ms. Within 10 ms of the stepwise increase in Ca(2+) concentration, we identified a distinct compact conformational state with a drastically different molecular dimension. This process is too fast to study with a conventional stopped-flow apparatus. The compact conformational state was also observed without mastoparan, indicating that the calmodulin forms a compact globular conformation by itself upon Ca(2+) binding. This new conformational state of calmodulin seems to regulate Ca(2+) binding and conformational changes in the N-terminal domain. On the basis of this finding, an allosteric mechanism, which may have implications in intracellular signal transduction, is proposed.
钙调蛋白通过结合 Ca(2+)发生特征性构象变化，使其能够与 300 多种靶蛋白结合，并调节所有真核细胞中的众多细胞内过程。我们使用时间分辨小角 X 射线散射技术结合笼锁 Ca(2+)的光解，测量钙调蛋白在 Ca(2+)和 mastoparan 结合时的构象变化。该测量系统涵盖 0.5-180ms 的时间范围。在 Ca(2+)浓度逐步增加的 10ms 内，我们确定了一种具有明显不同分子维度的独特紧凑构象状态。这个过程太快了，传统的停流装置无法研究。在没有 mastoparan 的情况下也观察到了这种紧凑的构象状态，表明钙调蛋白在结合 Ca(2+)时自身形成紧凑的球形构象。钙调蛋白的这种新构象状态似乎调节了 Ca(2+)结合和 N 端结构域的构象变化。基于这一发现，提出了一种变构机制，该机制可能对细胞内信号转导具有重要意义。
