Plant UDP-N-acetylglucosamine (UDP-GlcNAc) transporter (UGNT1) glycopeptide analysis

Glycosylation reactions require activated glycosyl donors in form of nucleotide sugars to drive processes such as post-translational protein modifications, glycolipid and polysaccharide biosynthesis. Most of these reactions occur in the Golgi requiring cytosolic-derived nucleotide sugars, which are actively transferred into the Golgi lumen by nucleotide sugar transporters. Here we present the identification of the plant UDP-N-acetylglucosamine (UDP-GlcNAc) transporter (UGNT1) indispensable for the delivery of a substrate for maturation of N-glycans and glycosyl inositol phosphorylceramides (GIPCs). Profiles of N-glycopeptides revealed that UGNT1 loss-of-function mutants are devoid of complex and hybrid N-glycans. Instead, most of the glycol-N-peptide population contained high mannose structures, representing the structure prior to the addition of the first GlcNAc in the Golgi. Our findings emphasize that the reference plant Arabidopsis contains a single UDP-GlcNAc transporter responsible for the maturation of complex N-glycans in the Golgi lumen.