Galectins are a general name proposed in 1994 for a subset of animal lectins widely distributed from lower invertebrates to mammals. In the last few years significant experimental data have been accumulated concerning their participation in different biological processes requiring carbohydrate recognition such as cell adhesion, cell growth regulation, inflammation, immunomodulation and cancer metastasis.
Galectins are defined as lectins having both galactose-binding ability and amino-acid sequences which characterize galectins. In general, galectins are soluble, and metal-independent in their activity. They also hold many features of cytoplasmic proteins, i.e., have no disulfide bridges, no sugar chains, no signal sequences, and in most cases their N-terminal amino acids are acetylated.
Evidence suggests that the galectins could be implicated in 'programmed cell death' of T-lymphocytes, a phenomena termed apoptosis. Cell death programming promotes immune tolerance by destroying hyper-reactive lymphocytes and terminating out-of-control immune responses. To put it simply, lymphocytes are susceptible to positive and negative selection by their interaction with galectins. T lymphocytes that fail to receive galectin stimulation ('neglected cells') undergo a default 'cell death' program. The remaining T cells are positively selected to survive.
Since these lectins usually require a thiol-reducing reagent for the maintenance of their activity, K. Drickamer once designated them as "S-type" lectins ("S" stands for SH-requiring), from the viewpoint of C-type lectins ("C" stands for Ca-requiring).
Galectins have been known to bind IgE on the cells of the pancreas which produce insulin. They also can bind the blood type A and B antigens at the same time.
1. Smetana K, Holikova Z, Klubal R, Bovin NV, Dvorankova B, Bartunkova J, Liu FT, Gabius HJ. Coexpression of binding sites for A(B) histo-blood group trisaccharides with galectin-3 and Lag antigen in human Langerhans cells. J Leukoc Biol 1999 Oct;66(4):644-9.