Relative Quantification of N-Glycopeptide Sialic Acid Linkage Isomers by Ion Mobility Mass Spectrometry
Xiaoxiao Feng, Hong Shu, Shu Zhang, Ye Peng, Lei Zhang, Xinyi Cao, Liming Wei, Haojie Lu
Abstract
Sialic acids decorate the surface of glycoproteins and play important roles in a variety of pathological processes. Although the mass spectrometry (MS) based linkage-specific analysis of sialylated N-glycopeptide is developing rapidly, quantitative analysis of these isomers still remains a challenge. Herein, we reported a novel quantitative strategy that can unambiguously identify and relatively quantify linkage-specific N-glycopeptides using ion mobility mass spectrometry (IM-MS). Without the assistance of derivatization, this method can relatively quantify sialic acid isomers of intact glycopeptides by using their characteristic fragment ions in IM-MS. Moreover, good linearity (R2 > 0.99) of relative quantification within a dynamic range of 2 orders of magnitude and high reproducibility (coefficient of variation (CV) < 10%, n = 3) were demonstrated. Finally, our results illustrated the aberrant sialylation of haptoglobin (Hp) in hepatocellular carcinoma (HCC), where the ratios of α2,3 to α2,6 sialylation of seven N-glycopeptides were found to be significantly altered (p < 0.01) in HCC individuals (n = 27) compared with healthy controls (n = 27).