Glycomic Analysis of Sialic Acid Linkages in Glycans Derived from Blood Serum Glycoproteins

A number of alterations to the normal glycomic profile have been previously described for a number of diseases and disorders, thus underscoring the medical importance of studying the glycans associated with proteins present in biological samples. An important alteration in cancer progression is an increased level of alpha 2,6-sialylation, which aids in increasing the metastatic potential of tumor cells. Here we report a glycomic method that selectively amidates alpha 2,6-linked sialic acids, while those that are alpha 2,3-linked undergo spontaneous lactonization. Following subsequent permethylation, MALDI-TOF MS analysis revealed that many sialylated glycans present on glycoproteins found in blood serum featured increased levels of alpha 2,6-sialylation in breast cancer samples. On the basis of the altered ratios of alpha 2,3-linked to alpha 2,6-linked sialic acids, many of these glycans became diagnostically relevant when they did not act as such indicators when based on traditional glycomic profiling alone.