Glycogen synthase (GYS1) is the central enzyme in muscle glycogen biosynthesis. GYS1 activity is inhibited by phosphorylation of its amino (N) and carboxyl (C) termini, which is relieved by allosteric activation of glucose-6-phosphate (Glc6P). We present cryo-EM structures at 3.0–4.0 Å resolution of phosphorylated human GYS1, in complex with a minimal interacting region of glycogenin, in the inhibited, activated and catalytically competent states. Phosphorylations of specific terminal residues are sensed by different arginine clusters, locking the GYS1 tetramer in an inhibited state via intersubunit interactions. The Glc6P activator promotes conformational change by disrupting these interactions and increases the flexibility of GYS1, such that it is poised to adopt a catalytically competent state when the sugar donor UDP-glucose (UDP-glc) binds. We also identify an inhibited-like conformation that has not transitioned into the activated state, in which the locking interaction of phosphorylation with the arginine cluster impedes subsequent conformational changes due to Glc6P binding. Our results address longstanding questions regarding the mechanism of human GYS1 regulation.

糖原合酶 (GYS1) 是肌糖原生物合成中的核心酶。GYS1 活性受其氨基 (N) 和羧基 (C) 末端磷酸化的抑制，而磷酸化葡萄糖 6-磷酸 (Glc6P) 的变构激活可缓解这种磷酸化。我们以 3.0–4.0 Å 的分辨率呈现磷酸化人 GYS1 的冷冻电镜结构，该结构与糖原蛋白的最小相互作用区域形成复合物，处于抑制、激活和催化能力状态。特定末端残基的磷酸化被不同的精氨酸簇感知，通过亚基间相互作用将 GYS1 四聚体锁定在抑制状态。Glc6P 激活剂通过破坏这些相互作用促进构象变化并增加 GYS1 的灵活性，因此当糖供体 UDP-葡萄糖 (UDP-glc) 结合时，它准备好采用催化能力状态。我们还确定了一种尚未转变为激活状态的抑制样构象，其中磷酸化与精氨酸簇的锁定相互作用阻碍了由于 Glc6P 结合而导致的后续构象变化。我们的结果解决了关于人类 GYS1 调节机制的长期存在的问题。