2001 Volume 13 Issue 73 Pages 533-549
Galectins are a group of relatively small lectins, whose ability to bind to β-galactosides is evolutionarily conserved among extensive organisms. In our previous studies, two distinct types of galectins, i.e., 32-kDa galectin and 16-kDa galectin were identified from the nematode Caenorhabditis elegans, and their molecular properties were characterized. More recently, however, the presence of a number of galectin-like genes became evident after completion of the genome project of this organism. Some of these candidate genes were systematically designated lec-1-11 for further study, where the previously characterized 32-kDa and 16-kDa galectins were renamed LEC-1 and LEC-6, respectively. Four members showing a closer relationship to the 32-kDa galectin were defined as lec-2-5, and the others showing novel features as lec-7-11. Open reading frames encoded by these genes were established through cDNA cloning, and registered to the genome/proteome databases. To elucidate their physiological functions, detailed sugar-binding specificity was examined by reinforced frontal affinity chromatography, and identification of endogenous glycoprotein receptors was attempted by the recently developed “glyco-catch” method. By the former method, affinities to a series of fluorescently labeled oligosaccharides were quantitatively determined rapidly and reliably. By the latter method, we identified genes that encode glycoproteins specifically recognized by C. elegans galectins by combination of conventional lectin-affinity technique and in silico database search. Notably, these two methods are directly applicable to the “glycome project” originally proposed by the authors, which aims at making a “list of glycoproteins” along with the concept of genome science. By the glycocatch method, the following three points will be clarified: 1) Which genes are expressed as glycoproteins. 2) Which sites among potential glycosylation sites are actually glycosylated. 3) Which kind of glycans (N-linked or O-linked, high-mannose type or complex type) are attached to these sites. As a result of the application of the glycomic approach to both soluble and detergent extracts of C. elegans and by using concanavalin A and galectin LEC-6 as probes, a substantial number of glycoprotein genes have been assigned. Thus, the strategy is considered to be fully applicable to more complex genome organisms (organisms in which the entire genome has been sequenced), such as humans. In the end, the authors propose a novel strategy to specify glycan structures.
