Towards high-throughput glycobiology

- Large-scale approaches for glycobiology

In conclusion, the hope for an increased pace of discovery in glycobiology, where progress has lagged because "carbohydrates are complex" [3], lies in several large-scale technologies now in the early stages of development. Continued progress is not without its problems. For example, the current versions of arrays contain only a very small fraction of all the carbohydrates found in nature [33]. A second issue is that the exact presentation of oligosaccharides is often important to achieve the 'cluster glycoside effect', whereby carbohydrate-binding interactions are specified by multiple simultaneous interactions that achieve both specificity and avidity [44,45]. Today's methods of attaching carbohydrates to an array, whereby they are spotted onto inflexible flat surfaces that have very different biophysical properties from the flexible peptide backbone of, say, CD34 (Figure 1a) or the spherical geometry of highly branched dendrimers [46], are unlikely to faithfully reproduce physiological binding.

Other nascent high-throughput methods, such as the automation of mass spectrometry, must also overcome significant barriers. The use of mass spectrometry in glycomics, for instance, is hampered in various ways: glycan databases are incomplete; that is, many of the oligosaccharides found in nature have not yet been isolated and characterized by mass spectrometry; the structural complexity of oligosaccharides limits current identification algorithms to structures of less than ten monosaccharides; and the identification of the correct oligosaccharide from many isomeric options remains a challenge [32]. Mass spectrometry must also overcome its aversion to sialic acids. In the past, this structurally diverse [12], negatively charged sugar has typically been removed to simplify analysis; the critical role of sialic acid in modulating the bioactivity of GM3 (Figure 1e) is but one of numerous examples that insist that this sugar cannot continue to be ignored. To end optimistically, these challenges, although appearing daunting today, will be overcome in the near future - within two to three years in one prediction [33] - if scientific curiosity and the potential multibillion dollar market for therapeutic glycoproteins continue to accelerate the current pace of technological development.