Nano-electrospray ionization time-of-flight mass spectrometry of gangliosides from human brain tissue

A general approach for the detection and structural elucidation of brain ga nglioside species GM1, GD1 and GT1 by nano-electrospray ionization quadrupo le time-of-flight (nanoESI-QTOF) mass spectrometry (MS), using combined dat a from MS and MS/MS analysis of isolated native ganglioside fractions in ne gative ion mode and their permethylated counterparts in the positive ion mo de is presented. This approach was designed to detect and sequence ganglios ides present in preparatively isolated ganglioside fractions from pathologi cal brain samples available in only very limited amounts. In these fraction s mixtures of homologue and isobaric structures are present, depending on t he ceramide composition and the position of the sialic acid attachment site . The interpretation of data for the entire sequence, derived from A, B, C and Y ions by nanoESI-QTOFMS/MS in the negative ion mode of native fraction s, can be compromized by ions arising from double and triple internal cleav ages. To distinguish between isobaric carbohydrate structures in gangliosid es, such as monosialogangliosides GM1a and GM1b, disialogangliosides GD1a, GD1b and GD1e or trisialogangliosides GT1b, GT1c and GT1d, the samples were analysed after permethylation in the positive ion nanoESI-QTOFMS/MS mode, providing set of data, which allows a clear distinction for assignment of o uter and inner fragment ions according to their m/z values. The fragmentati on patterns from native gangliosides obtained by low-energy collision induc ed dissociation (CID) by nanoESI-QTOF show common behaviour and follow inhe rent rules. The combined set of data from the negative and positive ion mod e low-energy CID can serve for the detection of structural isomers in mixtu res, and to trace new, not previously detected, components. Copyright (C) 2 001 John Wiley & Sons, Ltd.