平滑肌肌球蛋白磷酸化调节的分子机理

脊椎动物的平滑肌分布广泛，其功能失常与人类多种疾病有关。平滑肌的收缩功能依赖于平滑肌肌球蛋白(Smooth muscle Myosin，SmM)的马达活性：将水解ATP产生的化学能转化为机械能。SmM的马达活性受磷酸化调节，非磷酸化SmM的活力很低，磷酸化后活力极大地升高。但SmM磷酸化调节的分子机理尚不清楚。我们提出SmM磷酸化调节的尾部抑制-双头激活模型：非磷酸化SmM处于折叠状态，形成尾部对头部的抑制（可能还包括双头间的相互抑制）；磷酸化消除尾部抑制，同时促进了双头间的协同，使SmM处于伸展激活状态。因此，研究SmM磷酸化调节的关键是确定非磷酸化SmM如何形成折叠抑制状态的。本项目将利用真核细胞表达纯化得到野生型和突变的SmM蛋白，测定其马达活性，分析分子构象等生物物理特征，从而确定SmM各个功能基团在磷酸化调节中的作用,为建立SmM磷酸化调节的分子机理奠定基础。

Smooth muscle distributes widely in vertebrates, and its malfunction causes a number of human diseases. The contraction of smooth muscle depends on smooth muscle myosin (SmM) motor function - converting energy from ATP hydrolysis into mechanical movement. The motor function of SmM is regulated by phosphorylation of regulatory light chain. Unphosphorylated SmM has no motor activity, and phosphorylation of SmM stimulates its motor activity to the maximal level. Despite of decades study, the molecular mechanism of phosphorylation regulation of SmM has not been established. We propose a "tail-inhibition/ double-head activation model" for SmM regulation: the unphosphorylated SmM is in a folded conformation such that the tail-head interaction (maybe include head-head interaction) inhibits the motor function; phosphorylation not only abolishes the tail inhibition, but also induces the cooperation between the two heads of SmM, thus inducing an open conformation of SmM and stimulating its motor function to the maximal level. In the proposed study, we will investiage the roles of each structural domains of SmM on the phosphorylation regulation of SmM. We will use eukaryotic system to express wild type and mutant SmM and to characterize the motor functions and the biophyiscal properties of those SmM. This study will provide insight into the molecualr mechansim of SmM regulation by phosphorylation.