Identification of an unusually sulfated tetrasaccharide chondroitin/dermatan motif in mouse brain by combining chip-nanoelectrospray multistage MS2 -MS4 and high resolution MS.

Chondroitin sulfate (CS)/dermatan sulfate (DS) are often found in nature as hybrid glycosaminoglycan chains in various proteoglycans. In the recent years, several MS methods were developed for the determination of over-, regular-, and undersulfated CS/DS chains. In the present work, the released hybrid CS/DS isolated and purified from mouse brain were digested with chondroitin AC lyase. The depolymerized chains were separated by gel filtration chromatography. Collected tetrasaccharides were analyzed by fully automated (NanoMate robot) chip-based nanoESI high capacity ion trap multistage MS (MS2-MS4) recently introduced in glycosaminoglycan research by our laboratory. The obtained data were confirmed by high resolution MS screening and MS/MS performed on QTOF instrument. NanoMate-high capacity ion trap MS and QTOF MS screening revealed the presence in the mixture of oversulfated tetrasaccharides bearing three and four sulfate groups as well as traces of regularly and undersulfated hexamers. Additionally, several saturated species as either tetramers or hexamers exhibiting different sulfate content were discovered in the analyzed fraction. This diversity of the sulfation status indicates that the mouse brain might contain several types of proteoglycans. The molecular ions corresponding to trisulfated-[4,5-GlcA-GalNAc-IdoA-GalNAc] were subjected to multistage fragmentation by CID. Sequence analysis data allowed for the postulation of two rare structural motifs: [4,5-GlcA-GalNAc(4S)-IdoA(2S,3S)-GalNAc] and [4,5-GlcA-GalNAc-IdoA(2S,3S)-GalNAc(4S)], previously not reported in neural tissue.