KdpFABC is an ATP-dependent K+ pump that ensures bacterial survival in K+-deficient environments. Whereas transcriptional activation of kdpFABC expression is well studied, a mechanism for down-regulation when K+ levels are restored has not been described. Here, we show that KdpFABC is inhibited when cells return to a K+-rich environment. The mechanism of inhibition involves phosphorylation of Ser162 on KdpB, which can be reversed in vitro by treatment with serine phosphatase. Mutating Ser162 to Alanine produces constitutive activity, whereas the phosphomimetic Ser162Asp mutation inactivates the pump. Analyses of the transport cycle show that serine phosphorylation abolishes the K+-dependence of ATP hydrolysis and blocks the catalytic cycle after formation of the aspartyl phosphate intermediate (E1~P). This regulatory mechanism is unique amongst P-type pumps and this study furthers our understanding of how bacteria control potassium homeostasis to maintain cell volume and osmotic potential.

中文翻译：

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丝氨酸磷酸化调节 P 型钾泵 KdpFABC

KdpFABC 是一种依赖于 ATP 的 K+ 泵，可确保细菌在缺乏 K+ 的环境中存活。尽管对 kdpFABC 表达的转录激活进行了充分研究，但尚未描述当 K+ 水平恢复时下调的机制。在这里，我们展示了当细胞返回到富含 K+ 的环境时 KdpFABC 被抑制。抑制机制涉及 KdpB 上 Ser162 的磷酸化，可以在体外通过用丝氨酸磷酸酶处理逆转。将 Ser162 突变为丙氨酸会产生组成型活性，而拟磷 Ser162Asp 突变会使泵失活。运输循环分析表明，丝氨酸磷酸化消除了 ATP 水解对 K+ 的依赖性，并在形成天冬氨酰磷酸中间体 (E1~P) 后阻断了催化循环。