So far there is only one chimera Galectin in vertebrates called Galectin-3, it has several alternative names such as Mac-2 antigen, CBP35, and CBP30. Gal-3 predominantly exists as a monomer in solution but can self-associate via its N-terminal or C-terminal domains dependent on the ligand and the concentration of monomeric Gal-3.
Fig.1 Chimera Galectins and mode of self-association. (Ayona, et al., 2020)
The single gene LGALS3 codes the human Galectin-3 on chromosome 14. In its natural state, Galectin-3 is a two-domain protein with a proline-, glycine-, and tyrosine-rich repeat-rich N-terminal oligomerization domain and a carbohydrate-binding domain at the C-terminus. According to research, a bound Gal-3 molecule increases the binding of more Galectin-3 molecules. Gal-3 can interact with other proteins, such as Alix or Bcl-2, in addition to glycans, due to its N-terminal domain.
Intramolecular interactions between the carbohydrate recognition domain (CRD) and the N-terminal render the Galectin-3 molecule relatively inert in the closed conformer state. Two types of intermolecular interactions, N-terminal interactions, and CRD-CRD interactions, they are usually observed during multimerization and this results in an increased biological activity of Galectin-3.
Fig.2 Self-interactions in Galectin-3 bioactivation. (Suthahar, et al., 2018)
Galectin-3 has a variety of actions. Its internal forms often defend cells against apoptosis through processes unrelated to carbohydrates. For binding extracellularly with lactosamine-containing cell surface glycoconjugates via the CRD, the lectin mediates cell-cell and cell-matrix interactions and promotes apoptosis.
Involved in several inflammatory processes, neutrophil adherence and opsonization, monocyte chemoattraction, and mast cell activation, Galectin-3 is released during the differentiation of monocytes into macrophages. Gal-3 is considered to induce pathological remodeling by increasing fibroblast proliferation and collagen deposition when it is expressed more often in activated macrophages.
In recent years, research has found that Galectin-3 binding and cross-linking glycans on cell surface receptors, modulate signal transduction by novel carbohydrate-based recognition systems. In the cornea, Galectin-3 has been detected in the conjunctiva, trabecular meshwork, retina, and the lens where it plays a role in cell differentiation and adhesion of fiber cells through interaction with MP20, a member of the tetraspanin superfamily of integral membrane proteins.
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