# Human O-GlcNAcase catalytic-stalk dimer anchors flexible histone binding domains

## TL;DR

This study reveals the structure of human O-GlcNAcase (OGA-L) and shows how it binds to specific modified histone tails linked to open chromatin.

## Contribution

The study provides the first high-resolution structure of OGA-L and identifies its specific histone modification binding preferences.

## Key findings

- OGA-L forms a catalytic-stalk dimer with a resolution of 3.63 Å.
- OGA-L binds to histone modifications H3K36Me3 and H4K5,8,12,16Ac on nucleosomes.
- OGA-L does not bind to histone marks associated with repressive chromatin.

## Abstract

Although thousands of proteins are specifically O-GlcNAc modified, the molecular features recognized by the enzymes of O-GlcNAc cycling (OGT/OGA) remain poorly defined. Here we solved the structure of the long isoform of human OGA (OGA-L) by cryo-electron microscopy (cryo-EM) providing a physiologically relevant platform to study the enzyme. The catalytic-stalk dimer structure was solved to a resolution of 3.63 Å, and the locally refined OGA A- and B-chains to 2.98 Å and 3.05 Å respectively. Intriguingly, the cryo-EM structures also exhibit lower resolution densities associated with the pHAT domains, suggesting substantial flexion of these domains relative to the catalytic-stalk dimer. OGA-L binds to a small subset of the 384 modified histone tails on a commercial histone peptide array. High affinity binding of OGA-L was detected to recombinant DNA-containing mononucleosomes bearing the H3K36Me3 and H4K5,8,12,16Ac modifications. The OGA-L–H3K36Me3 interaction was further validated by traditional ChIP experiments in MEFs. Thus, OGA-L binds to two modified histone tails of nucleosomes linked to open chromatin, whereas it does not bind to marks associated with repressive chromatin. This model is consistent with OGA-L acting as a ‘reader’ of histone modifications linked to development, transcriptional activation, transposon silencing, and DNA damage repair.

Despite the widespread occurrence of O-GlcNAc modifications on proteins, the specific molecular interactions of O-GlcNAc cycling enzymes remain elusive. Here, the authors use cryo-electron microscopy to resolve the structure of human O-GlcNAcase (OGA-L) as a catalytic-stalk dimer, revealing its binding to modified histone tails.