Palladium-mediated enzyme activation suggests multiphase initiation of glycogenesis

Biosynthesis of glycogen, the essential glucose (and hence energy) storage molecule in humans, animals and fungi 1 , is initiated by the glycosyltransferase enzyme, glycogenin (GYG). Deficiencies in glycogen formation cause neurodegenerative and metabolic disease 2 – 4 , and mouse knockout 5 and inh...

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Published in:	Nature (London) Vol. 563; no. 7730; pp. 235 - 240
Main Authors:	Bilyard, Matthew K., Bailey, Henry J., Raich, Lluís, Gafitescu, Maria A., Machida, Takuya, Iglésias-Fernández, Javier, Lee, Seung Seo, Spicer, Christopher D., Rovira, Carme, Yue, Wyatt W., Davis, Benjamin G.
Format:	Journal Article
Language:	English
Published:	London Nature Publishing Group UK 01-11-2018 Nature Publishing Group
Subjects:	119/118 631/443/319 639/638/45/952 639/638/92/458/1524 82/58 Access control Activation Binding sites Biocatalysis Biosynthesis Catalysis Catalytic activity Chemical research Energy storage Enzyme Activation Enzymes Fungi Galactose - metabolism Glucose Glucose - biosynthesis Glucosyltransferases - metabolism Glycogen Glycogen synthesis Glycoproteins - metabolism Glycosylation Glycosyltransferase Humanities and Social Sciences Humans Intermediates Kinetics Letter Metabolic disorders Metabolism Mimicry multidisciplinary Mutation Oligosaccharides Organic chemistry Palladium Palladium - metabolism Palladium catalysts Polysaccharides Protein binding Protein C Proteins Reaction kinetics Science Science (multidisciplinary) Substrates Sugar Uridine Diphosphate - metabolism Glycogen Formation Glucosylation State Glycogenin (GYG) Quantum Mechanics/molecular Mechanics (QM/MM) Triphasic Kinetics
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Summary:	Biosynthesis of glycogen, the essential glucose (and hence energy) storage molecule in humans, animals and fungi 1 , is initiated by the glycosyltransferase enzyme, glycogenin (GYG). Deficiencies in glycogen formation cause neurodegenerative and metabolic disease 2 – 4 , and mouse knockout 5 and inherited human mutations 6 of GYG impair glycogen synthesis. GYG acts as a ‘seed core’ for the formation of the glycogen particle by catalysing its own stepwise autoglucosylation to form a covalently bound gluco-oligosaccharide chain at initiation site Tyr 195. Precise mechanistic studies have so far been prevented by an inability to access homogeneous glycoforms of this protein, which unusually acts as both catalyst and substrate. Here we show that unprecedented direct access to different, homogeneously glucosylated states of GYG can be accomplished through a palladium-mediated enzyme activation ‘shunt’ process using on-protein C–C bond formation. Careful mimicry of GYG intermediates recapitulates catalytic activity at distinct stages, which in turn allows discovery of triphasic kinetics and substrate plasticity in GYG’s use of sugar substrates. This reveals a tolerant but ‘proof-read’ mechanism that underlies the precision of this metabolic process. The present demonstration of direct, chemically controlled access to intermediate states of active enzymes suggests that such ligation-dependent activation could be a powerful tool in the study of mechanism. The mechanism of glycogenesis, initiated by glycogenin, involves three distinct kinetic phases, with the final phase involving a refining process where only glucose is tolerated as a substrate.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0028-0836 1476-4687
DOI:	10.1038/s41586-018-0644-7