Self-glucosylation of glycogenin, the initiator of glycogen biosynthesis, involves an inter-subunit reaction

Amy Lin, James Mu, Jie Yang, Peter J. Roach

Research output: Contribution to journalArticle

31 Scopus citations

Abstract

Glycogenin is a dimeric self-glucosylating protein involved in the initiation phase of glycogen biosynthesis. As an enzyme, glycogenin has the unusual property of transferring glucose residues from UDPglucose to itself, forming an α-1,4-glycan of around 10 residues attached to Tyr194. Whether this self-glucosylation reaction is inter- or intramolecular has been debated. We used site-directed mutagenesis of recombinant rabbit muscle glycogenin-1 to address this question. Mutation of highly conserved Lys85 to Gln generated a glycogenin mutant (K85Q) that had only 1-2% of the self- glucosylating activity of wild-type enzyme. Consistent with previous work, mutation of Tyr194 to Phe in a GST-fusion protein yielded a mutant, Y194F, that was catalytically active but incapable of self-glucosylation. The Y194F mutant was able to glucosylate the K85Q mutant. However, there was an initial lag in the self-glucosylation reaction that was abolished by preincubation of the two mutant proteins. The interaction between glycogenin subunits was relatively weak, with a dissociation constant inferred from kinetic experiments of around 2 μM. We propose a model for the glucosylation of K85Q by Y194F in which mixing of the proteins is followed by rate-limiting formation of a species containing both subunit types. The results provide the most direct evidence to date that the self-glucosylation of glycogenin involves an inter-subunit reaction.

Original languageEnglish (US)
Pages (from-to)163-170
Number of pages8
JournalArchives of Biochemistry and Biophysics
Volume363
Issue number1
DOIs
StatePublished - Mar 1 1999

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ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology

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