Glycosylation of the murine estrogen receptor-alpha.

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-alpha (mER-alpha) is modified by O-GlcNAc at Thr(575). Here we mutated mER-alpha to convert Thr(575) and Ser(576) 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-alpha, at Ser(10) and Thr(50) near the N-terminus. The major glycosylation sites are within or near PEST regions, suggesting that O-GlcNAc may regulate mER-alpha turnover.