Cryo-EM structure provides insights into the dimer arrangement of the O-linked \u03b2-N-acetylglucosamine transferase OGT

Richard W Meek,Gideon J Davies,Jil A Busmann,James N Blaza,Matthew G Alteen,David J Vocadlo

doi:10.1038/s41467-021-26796-6

Richard W Meek, Gideon J Davies + Show 4 more

Open Access

https://doi.org/10.1038/s41467-021-26796-6

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Journal: Nature Communications	Publication Date: Nov 11, 2021
Citations: 24	License type: open-access

Affiliation: Simon Fraser University, University of York

Abstract

The O-linked β-N-acetylglucosamine modification is a core signalling mechanism, with erroneous patterns leading to cancer and neurodegeneration. Although thousands of proteins are subject to this modification, only a single essential glycosyltransferase catalyses its installation, the O-GlcNAc transferase, OGT. Previous studies have provided truncated structures of OGT through X-ray crystallography, but the full-length protein has never been observed. Here, we report a 5.3 Å cryo-EM model of OGT. We show OGT is a dimer, providing a structural basis for how some X-linked intellectual disability mutations at the interface may contribute to disease. We observe that the catalytic section of OGT abuts a 13.5 tetratricopeptide repeat unit region and find the relative positioning of these sections deviate from the previously proposed, X-ray crystallography-based model. We also note that OGT exhibits considerable heterogeneity in tetratricopeptide repeat units N-terminal to the dimer interface with repercussions for how OGT binds protein ligands and partners.

Highlights

The O-linked β-N-acetylglucosamine modification is a core signalling mechanism, with erroneous patterns leading to cancer and neurodegeneration
Maps generated during data processing provided density into which only the catalytic domain appended to tetratricopeptide repeat (TPR) units 6-13.5 could be modelled, TPR units N-terminal of the dimer interface (TPRs 1–5) exhibited high heterogeneity, suggestive of flexibility in the TPR units of this region
Inspired by the work focussed on resolving structural heterogeneity in the catalytic domain of human γ-secretase, we attempted to capture some of the conformational states adopted by the N-terminal TPR units by careful classification of particles[20]

Summary

Introduction

The O-linked β-N-acetylglucosamine modification is a core signalling mechanism, with erroneous patterns leading to cancer and neurodegeneration. The O-linked GlcNAc is not elongated to form longer, complex glycans and instead cycles on and off the polypeptide target, more akin to phosphorylation than classical glycosylation[1] It is suspected crosstalk occurs between phosphorylation and O-GlcNAcylation[1]. The catalytic region alone can glycosylate short peptide targets, the TPRs are necessary for modification of full-length proteins, promoting peptide cleavage, and engaging in protein-protein interactions[9,10,11]. Underscoring their importance, detrimental mutations in the TPR region are linked to X-linked intellectual disability (XLID)[2].

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