Sialic acids play important roles in many physiological and pathological processes, including cancers, infection and blood diseases. Sialic acids are fragile and prone to fragmentation under electrospray ionization and matrix-assisted laser desorption/ionization conditions. Permethylation is a method of choice for sialic acid stabilization, but the harsh conditions during permethylation may lead to the decomposition of O-acetyl groups. Esterification or amidation in solution effectively protects sialic acids, yet, it is not trivial to separate glycans from their reagents. Quantitative analysis of glycans can be achieved by labeling their reducing end using fluorescent tags. However, loss of sialic acids during labeling is a major concern. In order to accurately quantify sialic acid substitutions and their linkages in biological samples appropriate modification schemes must be developed. In this study, we demonstrated the utility of sialic acid modification for the analysis of sialyl oligosaccharides and intact glycopeptides (Figure 1). Without modification, sialic acids were partially or completely lost during sample preparation, leading to the presence of false glycans or glycopeptides in the sample. The stabilized sialic acids not only result in accurate identification of sialylated glycans, but also enable distinguishment between α2,3 and α2,6-linked sialic acids, and improve the characterization of intact glycopeptides. The modification of sialic acids on the solid support facilitates analysis of glycans and their intact glycoproteins. We also demonstrated integration of the technique to a pipette-based format for automated sample preparation using a liquid handler.

Sialic acid modification: Stabilization and determination of linkages of sialylated glycans

254th National Meeting (2017)

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