Vertebrate lens alpha-crystallins are modified by O-linked N-acetylglucosamine.

摘要: Crystallins are structural proteins responsible for establishing the remarkable optical properties of lens. Yet many these highly conserved also expressed in nonocular tissues, where they have alternative functions apparently unrelated to their role Here we report that lens alpha-crystallins, some which function as heat-shock other modified with O-linked N-acetylglucosamine (O-GlcNAc). An vitro enzymatic assay transfers [3H]Gal terminal GlcNAc moieties labels alpha A and B crystallins homogenates from man, rhesus monkey, rat, cow, rhea (an ostrich-like bird). O-Linkage saccharide is demonstrated by sensitivity base-catalyzed beta-elimination resistance peptide:N-glycosidase F treatment. Chromatographic analyses products fast atom bombardment-mass spectrometry [3H]Gal-labeled tryptic peptides confirm structure. Isoelectric focusing bovine reveals presence O-GlcNAc on all four alpha-crystallin subunits, A1, A2, B1, B2. Electrospray mass demonstrates a single substitution A2. Gas-phase protein sequencing major radiolabeled peptide reveal attached subunits at serine 162. This post-translational modification may play an important molecular organization alpha-crystallin.