Tandem mass spectrometric determination of the 4S/6S sulfation sequence in chondroitin sulfate oligosaccharides

Chondroitin sulfate (CS) is a glycosaminoglycan consisting of repeating uronic acid, N-acetylgalactosamine sulfate disaccharide units [-UroA(beta1,3)-GalNAcS(beta1,4)]n. Chondroitin sulfate type A (CSA) contains glucuronic acid, and 90% of the GalNAc residues are sulfated at the 4-position with 10% at the 6-position. Chondroitin sulfate type C (CSC) contains glucuronic acid, and 90% of the GalNAc residues are sulfated at the 6-position with 10% sulfated at the 4-position. These molecules are fragile due to their high degree of sulfation and are challenging to analyze as a result. This work presents the first evidence that tandem mass spectrometry can be used for the determination of a CS oligosaccharide sequence with respect to the positions of GalNAc sulfation. Using this technique, it is possible to analyze individual components from mixtures, saving much purification effort. Oligosaccharides produced from CSA and CSC are used in this work to demonstrate that CID MS/MS can be used to distinguish positional sulfation isomers. For charge states where charge equals the number of sulfates, abundant odd-numbered Bn and Yn ions are observed. The percent total ion abundances of these ions indicate the position of sulfation.