Astbury Centre for Structural Molecular Biology, School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, UK.
Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark.
Nat Commun. 2022 Jun 11;13(1):3372. doi: 10.1038/s41467-022-31109-6.
Glycogen is the major glucose reserve in eukaryotes, and defects in glycogen metabolism and structure lead to disease. Glycogenesis involves interaction of glycogenin (GN) with glycogen synthase (GS), where GS is activated by glucose-6-phosphate (G6P) and inactivated by phosphorylation. We describe the 2.6 Å resolution cryo-EM structure of phosphorylated human GS revealing an autoinhibited GS tetramer flanked by two GN dimers. Phosphorylated N- and C-termini from two GS protomers converge near the G6P-binding pocket and buttress against GS regulatory helices. This keeps GS in an inactive conformation mediated by phospho-Ser641 interactions with a composite "arginine cradle". Structure-guided mutagenesis perturbing interactions with phosphorylated tails led to increased basal/unstimulated GS activity. We propose that multivalent phosphorylation supports GS autoinhibition through interactions from a dynamic "spike" region, allowing a tuneable rheostat for regulating GS activity. This work therefore provides insights into glycogen synthesis regulation and facilitates studies of glycogen-related diseases.
糖原是真核生物中葡萄糖的主要储备物，糖原代谢和结构的缺陷会导致疾病。糖原的合成涉及糖朊（glycogenin，GN）与糖原合酶（glycogen synthase，GS）的相互作用，GS 被葡萄糖-6-磷酸（glucose-6-phosphate，G6P）激活，被磷酸化失活。我们描述了 2.6Å分辨率的冷冻电镜结构，揭示了磷酸化的人 GS 四聚体被两个 GN 二聚体环绕。来自两个 GS 前体的磷酸化的 N-和 C-末端在 G6P 结合口袋附近汇聚，并支撑 GS 调节螺旋。这通过磷酸化丝氨酸 641 与复合“精氨酸窝”的相互作用，将 GS 保持在无活性构象，这种相互作用介导了 GS 的自动抑制。结构引导的突变破坏了与磷酸化尾巴的相互作用，导致基础/非刺激状态下 GS 活性增加。我们提出，多价磷酸化通过来自动态“刺”区的相互作用支持 GS 的自动抑制，从而为调节 GS 活性提供了一个可调变阻器。因此，这项工作为糖原合成的调控提供了深入的了解，并为糖原相关疾病的研究提供了便利。
