Lectins

Literature References: A group of proteins, widely distributed in nature, that have the ability to agglutinate erythrocytes and many other types of cells. Although their existence has been known since 1899, when Stillmark isolated a hemagglutinin from castor beans, the term "lectin" (from the Latin legere, to choose) was first introduced by W. C. Boyd and E. Slapleigh in Science 119, 419 (1954). It is now used to designate "a sugar-binding protein or glycoprotein of non-immune origin which agglutinates cells and/or precipitates glycoconjugates", I. J. Goldstein et al., Nature 285, 66 (1980). Lectins are found primarily in seeds of plants, but also occur in roots, leaves and bark. In addition, they are present in invertebrates such as clams, snails, and horseshoe crabs, and in several vertebrate species. The term phytohemagglutinin is used to refer to plant lectins. Important members of the lectin family include concanavalin A, abrin, ricin, q.q.v., as well as soybean agglutinin or SBA and wheat germ agglutinin or WGA. Lectins vary considerably in chemical and physical properties; only a limited number have been purified. Mol wts of 17,000 to 400,000 have been reported and most lectins have been found to contain Mn2+ and Ca2+. Nearly all lectins can be inhibited by free oligo- or monosaccharides of appropriate specificity. Although their physiological functions in plants or in other organisms are unknown, lectins exhibit a variety of unusual biological properties. Some are specific in their reactions with human blood groups; some induce mitosis in lymphocytes. WGA from wheat germ lipase has been shown to agglutinate mouse tumor cells more readily than cells from normal tissue: J. C. Aub et al., Proc. Natl. Acad. Sci. USA 50, 613 (1963); M. M. Burger, A. R. Goldberg, ibid. 57, 359 (1967). Soybean agglutinin and concanavalin A have been shown to agglutinate cell lines transformed by viral or chemical carcinogens: M. Inbar, L. Sachs, Nature 223, 710 (1969); eidem, Proc. Natl. Acad. Sci. USA 63, 1418 (1969); B. A. Sela et al., J. Membr. Biol. 3, 267 (1970). Some plant lectins mimic the direct effects of insulin on nuclear envelope phosphorylation: F. Purrello et al., Science 221, 462 (1983). Soybean agglutinin has also been used in bone marrow transplants in patients with severe combined immunodeficiency: Y. Reisner et al., Blood 61, 341 (1983). Reviews: N. Sharon, H. Lis, Science 177, 949-955 (1972); eidem, Annu. Rev. Biochem. 42, 541-574 (1973); L. Sequeira, Annu. Rev. Phytopathol. 16, 453-481 (1978). Book: Lectins: Biology, Biochemistry, Clinical Biochemistry vol. 1, T. C. Bog-Hansen, Ed. (de Gruyter, New York, 1981) 414 pp.