GALECTIN-1 FROM OVINE PLACENTA - AMINO-ACID-SEQUENCE, PHYSICOCHEMICALPROPERTIES AND IMPLICATIONS IN T-CELL DEATH

In the present study we report the amino-acid sequence, carbohydrate s pecificity and overall biochemical and physicochemical properties of g alectin-1, a beta-galactoside-binding lectin from ovine placenta. The complete amino-acid sequence, obtained by tryptic and chymotryptic dig estion, revealed that this carbohydrate-binding protein shares all the absolutely preserved and critical residues found in other members of the mammalian galectin-1 subfamily. Moreover, conformational changes i nduced by protein interaction with its specific disaccharide were inve stigated by fourth-derivative spectral analysis, intrinsic tryptophan fluorescence measurements and circular dichroism. The first two method s indicated changes in the environment of aromatic residues, in agreem ent with the role of Trp in carbohydrate binding. The quenching of the fluorescence emission upon addition of lactose, allowed us to calcula te the k(d) for its interaction with the galectin, which was 0.157 +/- 0.02 mM. The far-ultraviolet CD spectra. is consistent with the large extent of beta-sheet structure described for other galectins. Additio n of lactose produced no significant changes, suggesting that it cause s no modifications in the secondary structure of the lectin. In additi on, we explored its potential cell-growth inhibitory activity and impl ications in T-cell death. Finally, we also provide evidence showing th at antagonic properties of galectins-1 and -3 are reciprocally neutral ized in a natural mixture of both proteins, suggesting that they could play an important role in the regulation of cell proliferation and de ath, according to physiological requirements at particular development al stages of the placenta, thus allowing successful pregnancy to occur .