Glycosylation of the murine estrogen receptor-α

O-linked N-acetylglucosamine (O-GlcNAc) is a highly dynamic and abundant modification found on nuclear and cytoplasmic proteins of nearly all eukaryotes. O-GlcNAc addition is required for life at the single cell level and is analogous to protein phosphorylation in most respects. In a previous study (M.S. Jiang, G.W. Hart, A subpopulation of estrogen receptors are modified by O-linked N-acetylglucosamine. J. Biol. Chem. 270 (1997) 2421-2428), we demonstrated that a subpopulation of the murine estrogen receptor-α (mER-α) is modified by O-GlcNAc at Thr⁵⁷⁵. Here we mutated mER-α to convert Thr⁵⁷⁵ and Ser⁵⁷⁶ to Val and Ala, respectively. Surprisingly, this glycosylation-site mutant is still extensively modified by O-GlcNAc. Analyses of glycopeptides identified two additional sites of modification on mER-α, at Ser¹⁰ and Thr⁵⁰ near the N-terminus. The major glycosylation sites are within or near PEST regions, suggesting that O-GlcNAc may regulate mER-α turnover.