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

我们新确定了SERCA2b的几种低温EM结构，包括与两个结合的钙离子结合的高能E1P态和钙释放后的E1P态。E2P状态的数据集确定了一种新的构象，它不同于传统的E2P状态和随后的E2-PI状态，可以被认为是晚期钙结合中间体。低温EM结构表明，SERCA2b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制态。这些发现为酶的工作原理提供了重要的结构洞察；在反应中间体中形成了多个亚状态，包括一个与下一个中间体高度相似的亚状态，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.