Family of conserved S-type β-galactoside-binding lectins that bind to cell surface glycoconjugates. They are soluble and do not have transmembrane domains or signal sequences, although found associated with the outer cell surface. Some are homodimers (galectins 1–3), others are monomeric with two carbohydrate-binding sites. They have been identified in a large variety of metazoan phyla and are involved in many biological processes such as morphogenesis, control of cell death, immunological response, and cancer. Galectin-1 (galaptin, 135 aa) is a homodimer and is abundant in smooth and skeletal muscle. It mediates cell–cell and cell–substratum adhesion and plays a role in immune regulation. Recombinant galectin-1 will induce apoptosis in T cells. Galectin-2 (132 aa) binds to lymphotoxin-α. A SNP in galectin-2 is associated with susceptibility to myocardial infarction. Galectin-3 (IgE binding protein, Mac-2, e-BP, 250 aa) is usually considered proinflammatory and can act as an immunomodulator by inducing apoptosis in T cells. It is part of the AGE–receptor (RAGE) complex. Aberrant expression of galectin-3 involved in various aspects of tumour progression and p53-induced apoptosis is associated with transcriptional repression of Gal-3. Galectin-4 (323 aa) is monomeric with two carbohydrate binding sites, restricted to small intestine, colon, and rectum. Expression is altered in colorectal carcinoma. Galectins 5 and 6 have not been identified in humans although known in other mammals. Galectin-7 (136 aa) is confined to keratinocytes. Galectin 8 (prostate carcinoma tumour antigen-1, PCTA1, 316 aa) was isolated from a prostate carcinoma library and is related to galectin-4. Galectin-9 (355 aa) plays a role in thymocyte–epithelial interactions relevant to the biology of the thymus and an allelic variant, ecalectin, is a potent eosinophil chemoattractant produced by antigen-activated T cells. Galectin-10 (142 aa) is the Charcot–Leyden crystal protein. Galectin-12 and galectin-13 have also been identified.
Subjects: Medicine and Health.