Three-dimensional structure of a Streptomyces sviceus GNAT acetyltransferase with similarity to the C-terminal domain of the human GH84 O-GlcNAcase.

Yuan He,Johan P Turkenburg,Christian Roth,Gideon J Davies

doi:10.1107/s1399004713029155

Abstract

The mammalian O-GlcNAc hydrolysing enzyme O-GlcNAcase (OGA) is a multi-domain protein with glycoside hydrolase activity in the N-terminus and with a C-terminal domain that has low sequence similarity to known acetyltransferases, prompting speculation, albeit controversial, that the C-terminal domain may function as a histone acetyltransferase (HAT). There are currently scarce data available regarding the structure and function of this C-terminal region. Here, a bacterial homologue of the human OGA C-terminal domain, an acetyltransferase protein (accession No. ZP_05014886) from Streptomyces sviceus (SsAT), was cloned and its crystal structure was solved to high resolution. The structure reveals a conserved protein core that has considerable structural homology to the acetyl-CoA (AcCoA) binding site of GCN5-related acetyltransferases (GNATs). Calorimetric data further confirm that SsAT is indeed able to bind AcCoA in solution with micromolar affinity. Detailed structural analysis provided insight into the binding of AcCoA. An acceptor-binding cavity was identified, indicating that the physiological substrate of SsAT may be a small molecule. Consistent with recently published work, the SsAT structure further questions a HAT function for the human OGA domain.

Highlights

The addition of O-linked -N-acetylglucosamine (GlcNAc) to serine/threonine residues of nuclear and cytoplasmic proteins, known as O-GlcNAc modification (Torres & Hart, 1984), is an essential post-translational modification in higher eukaryotes
More recent work has shown that O-GlcNAc modification plays a role in the repression of gene expression by polycomb group proteins (Sinclair et al, 2009; Gambetta et al, 2009), further linking the modification through to epigenetic modulation of gene expression (Sakabe & Hart, 2010; reviewed by Sakabe et al, 2010)
We present the three-dimensional X-ray crystal structure of SsAT and a comparison with related GCN5related acetyltransferases (GNATs)-family acetyltransferases and their complexes, providing insight into acetyl coenzyme A (AcCoA) binding and highlighting key differences from the human OGA (hOGA) C-terminal domain

Summary

Introduction

The addition of O-linked -N-acetylglucosamine (GlcNAc) to serine/threonine residues of nuclear and cytoplasmic proteins, known as O-GlcNAc modification (Torres & Hart, 1984), is an essential post-translational modification in higher eukaryotes. Hundreds of proteins in the nuclear and cytoplasmic compartments have been reported to be O-GlcNAc modified (reviewed in Hart et al, 2007). The O-GlcNAc modification shares many similarities with protein phosphorylation and is at least partially reciprocal to phosphorylation (Wang et al, 2010; Hu et al, 2010). More recent work has shown that O-GlcNAc modification plays a role in the repression of gene expression by polycomb group proteins (Sinclair et al, 2009; Gambetta et al, 2009), further linking the modification through to epigenetic modulation of gene expression (Sakabe & Hart, 2010; reviewed by Sakabe et al, 2010)

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