Figure 1.

The galectin protein family. (a) Left panel: Cartoon of the anti-parallel beta-sheet structure forming the carbohydrate recognition domain of galectin-1 (in green). On the left, the interaction of a LacNAc (N-acetyllactosamine; blue-yellow) moiety in the binding groove is shown. Right panel: Overview of the 15 galectins that are expressed in humans. See text for explanation of the subgroups. (b) Cartoon depicting some of the key functions of galectins intra- and extracellularly. For more detailed information, refer to the reviews referred to in the main text. In the extracellular environment and on the cell surface, galectins can interact with glycoconjugates (blue-yellow) to facilitate, e.g., cell–cell interactions (I) and cell–extracellular matrix interactions (IV) to enable cell adhesion and migration. In addition, extracellular galectins can mediate interactions between molecules in the cell membrane to stimulate, e.g., lattice formation (II) and receptor dimerization (III), thereby promoting receptor cell surface retention and cell signaling. More recently, galectins were also found to heterodimerize with cytokines (V), affecting both galectin and cytokine activity. In the cytoplasm, galectins have been shown to engage in protein–protein interactions that facilitate, e.g., H-Ras nanocluster formation (VI) and signaling as well as cytokine secretion (VII). Finally, in the nucleus, galectins can interact with small nuclear ribonucleoproteins (VIII) thereby contributing to mRNA splicing.