selective protein O-glcNAcylation in cells by a proximity-directed O-GlcNAc transferase

O-Linked N-acetylglucosamine (O-GlcNAc) is a monosaccharide that plays an essential role in cellular signaling throughout the nucleocytoplasmic proteome of eukaryotic cells. Yet, the study of post-translational modifications like O-GlcNAc has been limited by the lack of strategies to induce O-GlcNAcylation of a target protein in cells. Here, we report a generalizable genetic strategy to induce O-GlcNAc to specific target proteins in cells using a nanobody as a proximity-directing agent fused to O-GlcNAc transferase (OGT). Fusion of a nanobody that recognizes GFP (nGFP) or a nanobody that recognizes the four-amino acid sequence EPEA (nEPEA) to OGT(4), a truncated form of OGT, yielded a nanobody-OGT(4) construct that selectively delivered O-GlcNAc to the target protein (e.g., JunB, cJun, Nup62) and reduced alteration of global O-GlcNAc levels in the cell. Chemical proteomics confirmed the selective increase in O-GlcNAc to the target protein by nanobody-OGT(4). Glycoproteomics on the target protein revealed similar glycosite selectivity between nanobody-OGT(4) or global elevation of O-GlcNAc. Finally, we demonstrate the ability to selectively target endogenous ⍺-synuclein for glycosylation in HEK293T cells. Thus, the use of nanobodies to redirect OGT substrate selection is a versatile strategy to induce glycosylation to desired target proteins in cells that will facilitate discovery of O-GlcNAc functions and provide a mechanism to engineer O-GlcNAc signaling. The proximity-directed OGT approach for protein-selective O-GlcNAcylation is readily translated to additional protein targets and nanobodies, and may constitute a generalizable strategy to control post-translational modifications in cells.