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bioRxiv · 10.1101/2021.11.12.468446

Molecular basis for the regulation of human glycogen synthase by phosphorylation and glucose-6-phosphate

McCorvie, T. J.·Loria, P. M.·Tu, M.·Han, S.·Shrestha, L.·Froese, D. S.·Ferreira, I. M.·Berg, A. P.·Yue, W. W.
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Abstract

Glycogen synthase (GYS1), in complex with glycogenin (GYG1), is the central enzyme of muscle glycogen biosynthesis, and its inhibition has been proposed as a therapeutic avenue for various glycogen storage diseases (GSDs). GYS1 activity is inhibited by phosphorylation of its N- and C-termini, which can be relieved by allosteric activation of glucose-6-phosphate. However, the structural basis of GYS1 regulation is unclear. Here, we present the first cryo-EM structures of phosphorylated human GYS1 complexed with a minimal interacting region of GYG1 in the inhibited, activated, and catalytically competent states at resolutions of 3.0-4.0 [A]. These structures reveal how phosphorylations of specific N- and C- terminal residues are sensed by different arginine clusters that lock the GYS1 tetramer complex in an inhibited state via inter-subunit interactions. The allosteric activator, glucose-6-phopshate, promotes a conformational change by disrupting these interactions and increases flexibility of GYS1 allowing for a catalytically competent state to occur when bound to the sugar donor UDP-glucose. We also identify an inhibited-like conformation that has not transitioned into the activated state, whereby the locking interaction of phosphorylation with the arginine cluster impedes the subsequent conformational changes due to glucose-6-phosphate binding. Finally, we show that the PP1 phosphatase regulatory subunit PPP1R3C (PTG) is recruited to the GYS1:GYG1 complex through direct interaction with glycogen. Our results address long-standing questions into the mechanism of human glycogen synthase regulation.

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McCorvie, T. J., Loria, P. M., Tu, M., Han, S., Shrestha, L., Froese, D. S., Ferreira, I. M., Berg, A. P., Yue, W. W.. 2021-11-13. Molecular basis for the regulation of human glycogen synthase by phosphorylation and glucose-6-phosphate. https://doi.org/10.1101/2021.11.12.468446

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