Quantitative proteomics identifies altered O‐GlcNAcylation of structural, synaptic and memory‐associated proteins in Alzheimer's disease

Protein modification by O‐linked β‐N‐acetylglucosamine (O‐GlcNAc) is emerging as an important factor in the pathogenesis of sporadic Alzheimer's disease (AD); however, detailed molecular characterization of this important protein post‐translational modification at the proteome level has been highly challenging, owing to its low stoichiometry and labile nature. Herein, we report the most comprehensive, quantitative proteomics analysis for protein O‐GlcNAcylation in postmortem human brain tissues with and without AD by the use of isobaric tandem mass tag labelling, chemoenzymatic photocleavage enrichment, and liquid chromatography coupled to mass spectrometry. A total of 1850 O‐GlcNAc peptides covering 1094 O‐GlcNAcylation sites were identified from 530 proteins in the human brain. One hundred and thirty‐one O‐GlcNAc peptides covering 81 proteins were altered in AD brains as compared with controls (q