OGT's inner circle: Protein interactions and functional impact

The modification of nuclear, cytoplasmic, and mitochondrial proteins by O-linked β-N-acetylglucosamine (O-GlcNAc) has emerged as an essential post-translational modification in mammals. More than 5000 human proteins are subject to O-GlcNAcylation, influencing key cellular processes such as signal transduction, epigenetic regulation, transcription, translation, and bioenergetics. Dysregulation of this modification has been implicated in a wide range of diseases, including metabolic disorders, cancer, neurodegeneration, ischemic injury, and heart failure. O-GlcNAc-cycling is orchestrated by two enzymes: the O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), which catalyze the addition and removal of O-GlcNAc, respectively. A central challenge in the field is understanding how this minimal enzymatic machinery achieves such broad substrate specificity. It is hypothesized that OGT's functional versatility is mediated through interactions with a diverse network of protein partners that act as adaptors, scaffolds, or substrates, thereby directing its localization, modulating its activity, and shaping its substrate selectivity. In this review, we discuss key interactors and their functional impact on OGT. We also explore how post-translational modifications and substrate availability contribute to OGT regulation and specificity.