Abstract
Cells encode information in the sequence of biopolymers, such as nucleic acids, proteins, and glycans. Although glycans are essential to all living organisms, surprisingly little is known about the “sugar code” and the biological roles of these molecules. The reason glycobiology lags behind its counterparts dealing with nucleic acids and proteins lies in the complexity of carbohydrate structures, which renders their analysis extremely challenging. Building blocks that may differ only in the configuration of a single stereocenter, combined with the vast possibilities to connect monosaccharide units, lead to an immense variety of isomers, which poses a formidable challenge to conventional mass spectrometry. In recent years, however, a combination of innovative ion activation methods, commercialization of ion mobility–mass spectrometry, progress in gas-phase ion spectroscopy, and advances in computational chemistry have led to a revolution in mass spectrometry-based glycan analysis. The present review focuses on the above techniques that expanded the traditional glycomics toolkit and provided spectacular insight into the structure of these fascinating biomolecules. To emphasize the specific challenges associated with them, major classes of mammalian glycans are discussed in separate sections. By doing so, we aim to put the spotlight on the most important element of glycobiology: the glycans themselves.
Highlights
Carbohydrates often referred to as glycans are the most abundant organic polymers found on Earth
The present review focuses on developments accomplished in the past 15 years in the field of electrospray ionization−mass spectrometry (ESI-MS) based techniques for the structural characterization of glycans
Ion mobility spectrometry (IMS) is a gas-phase electrophoretic separation technique, widely employed as a stand-alone method for the detection of drugs, explosives, and chemical warfare agents.[97−99] It has a long history as part of ion mobility−mass spectrometry (IM-MS) couplings, with applications in fields as diverse as molecular physics and structural biology.[100−114] Since the commercialization of the first integrated instruments, IMMS has gained remarkable popularity in bioanalytical chemistry[115−126] and become a key element of the glycomics toolbox.[23,29,34,35,127−130] Glycan isomers often exhibit identical fragment ion spectra, impeding their tandem MS-based distinction, while the presence of multiple isomers in a mixture calls for efficient separations
Summary
Carbohydrates often referred to as glycans are the most abundant organic polymers found on Earth They are essential to all known living organisms and regulate a variety of vital functions.[1] Structurally, glycans are composed of monosaccharide building blocks linked together via glycosidic bonds. High energy activation methods such as electron-based dissociation (ExD)[30,31] or ultraviolet photodissociation (UVPD)[32] help to disentangle complex oligosaccharide structures based on more informative fragmentation patterns Approaches such as ion mobility spectrometry (IMS) and gas-phase spectroscopy, on the other hand, are directly sensitive to the structure of the investigated molecule.[33−36] Here we discuss recent developments in the structural analysis of glycans and glycoconjugates using MSbased techniques. Sections dedicated to the different molecule classes may be read independently of each other, and the reader is encouraged to freely select those in their interest in any desired order
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