New mechanisms of action of human calcium ATPase SERCA2b revealed by cryo-EM analysis

我们新确定了SERCA 2b的几种cryo-EM结构，包括具有两个结合的Ca离子的高能E1 P状态和Ca释放后立即的后E1 P状态。E2 P状态的数据集鉴定了不同于常规E2 P状态和随后的E2-Pi状态的新构象，其可以被视为晚期Ca未结合的中间体。cryo-EM结构表明SERCA 2b在反应中采用多种构象，并产生与下一个中间体非常相似的预形成状态。这些发现为酶如何工作提供了重要的结构见解;在反应中间体中形成多个子状态，包括一个与下一个中间体高度相似的子状态，以促进过渡步骤，从而有效地驱动催化循环。

We newly determined several cryo-EM structures of SERCA2b, including a high-energy E1P state with two bound Ca ions and the post-E1P state immediately after Ca release. The dataset in E2P state identified a new conformation that differs from the conventional E2P state and the subsequent E2-Pi state that can be regarded as a late-stage Ca-unbound intermediate. The cryo-EM structures suggested that SERCA2b adopts multiple conformations in reaction and generates preformed states closely resembling the next intermediate. These findings provide essential structural insight into how enzymes work; multiple sub-states, including one highly similar to a next intermediate, are formed in a reaction intermediate to facilitate the transition step and thereby drive the catalytic cycle efficiently.