Characterization of oligo- and polysialic acids by MALDI-TOF-MS.

Oligo- and polysialic acids (oligo/polySia) are characterized by a high diversity in nature due to the different types of sialic acids linked to each other and glycosidic linkages involved. Considering the methods that are presently available for analysis of oligo/polySia chains, only fluorometric anion-exchange high-performance liquid chromatography (HPLC) analysis, fluorometric C7/C9 detection, and western blotting are applicable to small amounts of material. Here we describe an alternative technique using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry after on-target lactonization to characterize different sialic acid polymers. The MS-based method allows a rapid, highly sensitive, and unambiguous identification of native as well as fluorescently labeled sialic acid polymers without the need of standard substances due to exact mass determination. PolySia chains with at least 100 sialic moieties are easily detectable, and in addition, potential modifications of hydroxyl groups by, for instance, acetyl residues can be precisely registered. Based on different lactonization characteristics, alpha2-8- and alpha2-9-linked oligo/polySia can be distinguished. Furthermore, this method can be combined with fluorometric derivatization and HPLC separation.