Thin-layer chromatography, overlay technique and mass spectrometry: a versatile triad advancing glycosphingolipidomics

Abstract

Much effort is currently invested in the development of mass spectrometry-based strategies for investigating the entirety of glycosphingolipids (GSLs) of a certain cell type, tissue, organ or body encompassing the respective glycosphingolipidome. As part of the investigation of the vertebrate glycosphingolipidome, GSL analysis is undergoing rapid expansion owing to the application of novel mass spectrometry techniques acting as the linchpin in the network of collaborations challenged to unravel structural and functional aspects of GSLs. Difficulties may arise in the determination of the exact structures of GSLs due to the heterogeneity of the sugar moiety varying in the number and sequence of monosaccharides, and their anomeric configuration and linkage type, which make up the principal items of the glyco code of biologically active carbohydrate chains. The ceramide variability caused by the diversity of the long-chain amino alcohol and the fatty acid, which both may vary in chain length, degree of unsaturation, and type and number of substituents, further contributes to the increasing number of possible GSL species. In view of this heterogeneity, a single-method analytical mass spectrometry (MS) technique without auxiliary tools yields limited data, providing only partial structural information of individual GSLs in complex mixtures. Approaching this challenge, current advances on a triad system matching three complementary methods are described in this review: (i) silica gel based TLC separation of GSLs, (ii) their overlay detection on the TLC plate (mostly based on antibody-mediated recognition), and (iii) direct and indirect MS based structural characterization, i.e. directly on the TLC plate or in lipid extracts from silica gel. We will focus on recent improvements by employing antibodies, AB(5) toxins and bacteria for direct IR-MALDI-o-TOF MS and indirect ESI-QTOF MS analysis of GSLs. We believe that the combinatorial approach using conventional TLC and modern mass spectrometry provides a developmental advance in exploring the glycosphingolipidome of biological material.