Berger C E, Fagnant P M, Heizmann S, Trybus K M, Geeves M A
Department of Biosciences, University of Kent, Canterbury CT2 7NJ, United Kingdom.
J Biol Chem. 2001 Jun 29;276(26):23240-5. doi: 10.1074/jbc.M100524200. Epub 2001 Apr 11.
Light chain phosphorylation is the key event that regulates smooth and non-muscle myosin II ATPase activity. Here we show that both heads of smooth muscle heavy meromyosin (HMM) bind tightly to actin in the absence of nucleotide, irrespective of the state of light chain phosphorylation. In striking contrast, only one of the two heads of unphosphorylated HMM binds to actin in the presence of ADP, and the heads have different affinities for ADP. This asymmetry suggests that phosphorylation alters the mechanical coupling between the heads of HMM. A model that incorporates strain between the two heads is proposed to explain the data, which have implications for how one head of a motor protein can gate the response of the other.
轻链磷酸化是调节平滑肌和非肌肉肌球蛋白II ATP酶活性的关键事件。我们在此表明，在没有核苷酸的情况下，平滑肌重酶解肌球蛋白（HMM）的两个头部都紧密结合肌动蛋白，而与轻链磷酸化状态无关。与之形成鲜明对比的是，在存在ADP的情况下，未磷酸化的HMM的两个头部中只有一个与肌动蛋白结合，并且两个头部对ADP的亲和力不同。这种不对称性表明磷酸化改变了HMM头部之间的机械偶联。我们提出了一个包含两个头部之间应变的模型来解释这些数据，这些数据对于一种运动蛋白的一个头部如何控制另一个头部的反应具有启示意义。
