Elucidation of the mechanism of interaction of sheep spleen galectin-1 with splenocytes and its role in cell-matrix adhesion.

The binding of a 14 kDa beta-galactoside animal lectin to splenocytes has been studied in detail. The binding data show that there are two classes of binding sites on the cells for the lectin: a high-affinity site with a K(a) ranging from 1.1 x 10(6) to 5.1 x 10(5) M (-1) and a low affinity binding site with a K(a) ranging from 7.7 x 10(4) to 3.4 x 10(4) M (-1). The number of receptors per cell for the high- and low-affinity sites is 9 +/- 3 x 10(6) and 2.5 +/- 0.5 x 10(6), respectively. The temperature dependence of the K value yielded the thermodynamic parameters. The energetics of this interaction shows that, although this interaction is essentially enthalpically driven (DeltaH - 21 kJ lambdamol(-1)) for the high-affinity sites, there is a very favorable entropy contribution to the free energy of this interaction (-TDeltaS - 17.5 Jmol(-1)), suggesting that hydrophobic interaction may also be playing a role in this interaction. Lactose brought about a 20% inhibition of this interaction, whereas the glycoprotein asialofetuin brought about a 75% inhibition, suggesting that complex carbohydrate structures are involved in the binding of galectin-1 to splenocytes. Galectin-1 also mediated the binding and adhesion of splenocytes to the extracellular matrix glycoprotein laminin, suggesting a role for it in cell-matrix interactions. Copyright 2000 John Wiley & Sons, Ltd.