Genetics, Molecular Biology And Evolution

The last two decades have witnessed a revolution in our knowledge of the genetics and the molecular biology of lectins. and provided insights into their evolution. Some 200 lectins from diverse sources have been cloned and many have been expressed in heterologous systems. Molecular analysis of the genes obtained, whether as cDNA or genomic DNA, unveiled the primary structures of the corresponding lectins when these structures were not available from conventional techniques of protein sequencing, and in other cases have supplemented information obtained by such techniques. In addition, essential information has become available on lectin biosynthesis and novel pathways of protein processing have been encountered. Cloning has also led to the discovery of new lectins, as well as proteins that share sequence similarity with particular lectins but are devoid of carbohydrate binding activity. Examples are arcelin from the seeds of Phaseolus vulgaris, the lectin-related proteins in the roots of garlic and in the bark of elderberry (Van Damme et al., 1998b), and the galectin-related interfiber protein (GRIFIN) in the lens of the rat (Ogden et al., 1998). An extreme case is the close to 400 C-type lectin-like domains (CTLDs) that have been identified in a wide range of animals, from worms to mammals, roughly 180 of them in the genome of the nematode Caenorhabditis elegans alone, representing the seventh most common protein domain identified in this organism (Drickamer & Dodd, 1999).