STRUCTURAL AND FUNCTIONAL-CHARACTERIZATION OF A NOVEL TUMOR-DERIVED RAT GALECTIN-1 HAVING TRANSFORMING GROWTH-FACTOR (TGF) ACTIVITY - THE RELATIONSHIP BETWEEN INTRAMOLECULAR DISULFIDE BRIDGES AND TGF ACTIVITY

Previously we demonstrated that overexpression of a beta-galactoside b inding protein, galectin-1, caused the transformation of BALB3T3 fibro blast cells [Yamaoka, K., Ohno, S., Kawasaki, H., and Suzuki, K. (1991 ) Biochem, Biophys, Res, Commun, 179, 272-279], We have now studied th e structure-function relationships between the sugar-binding activity and the mitogenic activity of galectin-1 purified from an avian sarcom a virus-transformed rat NRK cell line, 77N1. The purified galectin-1 ( t-galectin-1) had potent mitogenic activity in BALB3T3 cells, but no s ugar-binding activity, Treatment of t-galectin-1 with 2-mercaptoethano l decreased its mitogenic activity, but resulted in the appearance of a sugar binding activity, Chemical modification of sulfhydryl groups i n purified t-galectin-1 with [C-14]-iodoacetamide suggested the presen ce of intramolecular disulfide bonds, MALDI-TOF mass spectrometric ana lysis of the native and reduced forms of the tryptic peptides from t-g alectin-1 showed that t-galectin-1 has two intramolecular disulfide bo nds (Cys2-Cys16 and Cys42-Cys60). These studies suggest that these int ramolecular disulfide bonds of t-galectin-1 are essential for its mito genic activity and that the different activities may be regulated by s tructural changes caused by intramolecular disulfide bond-breakage.