Understanding O-GlcNAc transferase (OGT): Every amino acid matters

O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) mediate all the "writing" and "erasing" of intracellular O-GlcNAc modification events on the serine or threonine residues of proteins. Decades of investigations have revealed many O-GlcNAc substrates, spanning almost all areas of biological research. The question remains, however: why is there only one OGT? Here, we provide a tentative answer to the "one OGT" question. We propose that OGT is a sensor of various biological stimuli and responds accordingly by incurring post-translational modifications (PTMs) or through its short linear motifs (SLiMs). Both PTMs and SLiMs reside in its intrinsic disordered regions, tetratricopeptide repeats, or catalytic domains and contribute to altering its enzymatic activity, protein-protein interaction, subcellular localization, and protein stability. OGA follows the same pattern, although to a lesser extent. We propose that OGT, or OGA, can sense biological cues and, via its PTMs or SLiMs, adjust the downstream OGT interactome and O-GlcNAcome correspondingly.