Abstact

Epidermal growth factor (EGF) domain-specific O-linked N-acetylglucosamine transferase (EOGT), a glycosyltransferase (GT) 61 family member, catalyzes O-N-acetylglucosamine (O-GlcNAc) transfer from uridine diphosphate (UDP)-GlcNAc to serine or threonine residues within EGF domains in the endoplasmic reticulum. In this study, we determined the crystal structure of the EOGT-UDP complex and identified the critical residues mediating their interactions, which were validated via site-directed mutagenesis and enzyme activity assays. These residues were conserved in EOGT orthologs across metazoans, and UDP binding occurred independently of divalent metal ions and the canonical Asp-X-Asp motif. Although EOGT catalyzes O-GlcNAcylation, similar to O-GlcNAc transferase (OGT), it shares little sequence similarity with OGT and belongs to a distinct GT family. Instead, EOGT is more closely related to protein O-linked-mannose beta1,4-N-acetylglucosaminyltransferase 2 (POMGNT2). Structural comparison with POMGNT2 revealed a conserved triad of one asparagine and two arginine residues, the N-R-R constellation. These elements were conserved across metazoans and green plants (Viridiplantae), suggesting a unifying mechanism of UDP recognition and providing a framework to interpret disease-associated EOGT mutations and assess the evolution of catalytically active GT61 family enzymes.