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LC-MS/MS characterization of combined glycogenin-1 and glycogenin-2 enzymatic activities reveals their self-glucosylation preferences.

Journal article
Authors Johanna Nilsson
Adnan Halim
Erik Larsson
Ali-Reza Moslemi
Anders Oldfors
Göran Larson
Jonas Nilsson
Published in Biochimica et biophysica acta
Volume 1844
Issue 2
Pages 398-405
ISSN 0006-3002
Publication year 2014
Published at Institute of Biomedicine, Department of Clinical Chemistry and Transfusion Medicine
Institute of Biomedicine, Department of Pathology
Institute of Biomedicine, Department of Medical Biochemistry and Cell Biology
Pages 398-405
Language en
Links dx.doi.org/10.1016/j.bbapap.2013.11...
Subject categories Clinical Medicine

Abstract

Glycogen synthesis is initiated by self-glucosylation of the glycosyltransferases glycogenin-1 and -2 that, in the presence of UDP-glucose, form both the first glucose-O-tyrosine linkage, and then stepwise add a series of α1,4-linked glucoses to a growing chain of variable length. Glycogen-1 and -2 coexist in liver glycogen preparations where the proteins are known to form homodimers, and they also have been shown to interact with each other. In order to study how glycogenin-1 and -2 interactions may influence each other's glucosylations we setup a cell-free expression system for in vitro production and glucosylation of glycogenin-1 and -2 in various combinations, and used a mass spectrometry based workflow for the characterization and quantitation of tryptic glycopeptides originating from glycogenin-1 and -2. The analysis revealed that the self-glucosylation endpoint was the incorporation of 4-8 glucose units on Tyr 195 of glycogenin-1, but only 0-4 glucose units on Tyr-228 of glycogenin-2. The glucosylation of glycogenin-2 was enhanced to 2-4 glucose units by the co-presence of enzymatically active glycogenin-1. Glycogenin-2 was, however, unable to glucosylate inactive glycogenin-1, at least not an enzymatically inactivated Thr83Met glycogenin-1 mutant, recently identified in a patient with severe glycogen depletion.

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