Random glycopeptide bead libraries for seromic biomarker discovery

Identification of disease specific biomarkers is important to address early diagnosis and management of disease. Aberrant post-translational modifications (PTM) of proteins such as O-glycosylations (O-PTMs) are emerging as triggers of autoantibodies that can serve as sensitive biomarkers. Here we have developed a random glycopeptide bead library screening platform for detection of autoantibodies and other binding proteins. Libraries were build on biocompatible PEGA beads including a safety-catch C-terminal amide linker (SCAL) that allowed mild cleavage conditions (I(2)/NaBH(4) and TFA) for release of glycopeptides and sequence determination by ESI-MS(n). As proof-of principle, tumor specific glycopeptide reporter epitopes were built-in into the libraries and were detected by tumor specific monoclonal antibodies and autoantibodies from cancer patients. Sequenced and identified glycopeptides were re-synthesized at preparative scale by automated parallel peptide synthesis and printed on microarrays for validation and broader analysis with larger sets of sera. We further showed that chemical synthesis of the monosaccharide O-glycopeptide library (Tn-glycoform) could be diversified to other tumor glycoforms by on-bead enzymatic glycosylation reactions with recombinant glycosyltransferases. Hence, we have developed a high-throughput flexible platform for rapid biomarker discovery O-glycopeptides and the method has applicability in other types of assays like lectin/antibody/enzyme specificity studies as well as investigation of other PTMs

Lipochitin Oligosaccharides Immobilized through Oximes in Glycan Microarrays Bind LysM Proteins

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