Structure changs in transport sites by phosphoenzyme isomerization of sarcoplasmic reticulum Ca2+ pump

Ca 2+泵在Ca 2+转运循环中形成磷酸化中间体（EP），在EP异构化过程中，胞质结构域的结构变化传递到膜结构域的Ca 2+位点，使Ca 2+转运到胞腔中。结果表明，M2的各个部分及其连接体在ATP水解和Ca ~（2+）转运的偶联、EP水解、因此，M2及其连接体的结构变化具有区域特异性和步骤特异性，从而耦合了Ca 2+转运的催化位点和转运位点的结构事件。

Ca2+ pump forms phosphorylated intermediates (EP) in Ca2+ transport cycle.In EP isomerization structural changes in cytoplasmic domains are transmitted to the Ca2+ sites in the membrane domain to tranlocate Ca2+ into lumen.Functional roles of helix M2 and its linker with the cytoplasmic Actuator-domain are explored by mutation study.The results show that each portion of M2 and its linker function in coupling of ATP hydrolysis and Ca2+ transport,EP hydrolysis, open-close of cytoplasmic and luminal Ca2+-gate,and Ca2+-induced activation of unphosphorylated intermediate.Therefore,the structural changes of M2 and its linker play critical roles region-specifically and step-specifically, and thereby couple the structural events in the catalytic site and the transport sites for the Ca2+ transport.