Biochemical characterization of Neurospora crassa glycogenin (GNN), the self-glucosylating initiator of glycogen synthesis

Renato M. De Paula, Wayne A. Wilson, Peter J. Roach, Héctor F. Terenzi, Maria Célia Bertolini

Research output: Contribution to journalArticle

5 Scopus citations

Abstract

Glycogenin acts in the initiation step of glycogen biosynthesis by catalyzing a self-glucosylation reaction. In a previous work [de Paula et al., Arch. Biochem. Biophys. 435 (2005) 112-124], we described the isolation of the cDNA gnn, which encodes the protein glycogenin (GNN) in Neurospora crassa. This work presents a set of biochemical and functional studies confirming the GNN role in glycogen biosynthesis. Kinetic experiments showed a very low GNN K m (4.41 μM) for the substrate UDP-glucose. Recombinant GNN was produced in Escherichia coli and analysis by mass spectroscopy identified a peptide containing an oligosaccharide chain attached to Tyr196 residue. Site-directed mutagenesis and functional complementation of a Saccharomyces cerevisiae mutant strain confirmed the participation of this residue in the GNN self-glucosylation and indicated the Tyr198 residue as an additional, although less active, glucosylation site. The physical interaction between GNN and glycogen synthase (GSN) was analyzed by the two-hybrid assay. While the entire GSN was required for full interaction, the C-terminus in GNN was more important. Furthermore, mutation in the GNN glucosylation sites did not impair the interaction with GSN.

Original languageEnglish (US)
Pages (from-to)2208-2214
Number of pages7
JournalFEBS Letters
Volume579
Issue number10
DOIs
StatePublished - Apr 11 2005

Keywords

  • Glycogen
  • Glycogenin
  • Mass spectrometry
  • Neurospora crassa
  • Site-directed mutagenesis
  • Yeast complementation

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Molecular Biology

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