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 b een 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 recep tors 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 sh ows that, although this interaction is essentially enthalpically driven (De lta H - 21 kJ lambda mol(-1)) for the high-affinity sites, there is a very favorable entropy contribution to the free energy of this interaction (-T D elta S - 17.5 Jmol(-1)), suggesting that hydrophobic interaction may also b e playing a role in this interaction. Lactose brought about a 20% inhibitio n of this interaction, whereas the glycoprotein asialofetuin brought about a 75 % inhibition, suggesting that complex carbohydrate structures are invo lved in the binding of galectin-1 to splenocytes, Galectin-1 also mediated the binding and adhesion of splenocytes to the extracellular matrix glycopr otein laminin, suggesting a role for it in cell-matrix interactions. Copyri ght (C) 2000 John Wiley & Sons, Ltd.