Phage display uncovers a sequence motif that drives polypeptide binding to a conserved regulatory exosite of O-GlcNAc transferase

Abstract

The modification of nucleocytoplasmic proteins by O-linked N-acetylglucosamine (O-GlcNAc) is an important regulator of cell physiology. O-GlcNAc is installed on over a thousand proteins by just one enzyme, O-GlcNAc transferase (OGT). How OGT is therefore regulated is therefore a topic of interest. To gain insight into these questions, we used OGT to perform phage display selection from an unbiased library of [~]108 peptides of 15 amino acids in length. Following rounds of selection and deep mutational panning we identified a high-fidelity peptide consensus sequence, [Y/F]-x-P-x-Y-x-[I/M/F], that drives peptide binding to OGT. Peptides containing this sequence bind to OGT in the high nanomolar to low micromolar range and inhibit OGT in a non-competitive manner with low micromolar potencies. X-ray structural analyses of OGT in complex with a peptide containing this motif surprisingly revealed binding to an exosite proximal to the active site of OGT. This structure defines the detailed molecular basis driving peptide binding and explains the need for specific residues within the sequence motif. Analysis of the human proteome revealed this motif within 52 nuclear and cytoplasmic proteins. Collectively, these data suggest an unprecedented mode of regulation of OGT by which polypeptides can bind to this exosite to cause allosteric inhibition of OGT through steric occlusion of its active site. We expect these insights will drive improved understanding of the regulation of OGT within cells and enable the development of new chemical tools to exert fine control over OGT activity. SIGNIFICANCE STATEMENTThousands of proteins within humans are modified by the monosaccharide N-acetylglucosamine (O-GlcNAc). O-GlcNAc regulates cellular physiology and is being pursued to create therapeutics. Remarkably, only one enzyme, O-GlcNAc transferase (OGT), installs O-GlcNAc and its regulation is poorly understood. By affinity selection using a vast peptide library, we uncover an amino acid sequence motif that drives binding of polypeptides to OGT. An OGT-peptide complex shows how this motif binds to an allosteric site proximal to the active site and inhibits OGT in an unprecedented manner. Given the distribution of this sequence motif within the human proteome proteins containing this motif likely regulate the activity of OGT, outlining a new mode by which OGT is controlled and opening new avenues for research.