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 binding protein, galectin-1, caused the transformation of BALB3T3 fibroblast cells [Yamaoka, K., Ohno, S., Kawasaki, H., and Suzuki, K. (1991) Biochem. Biophys. Res. Commun. 179, 272-279]. We have now studied the structure-function relationship between the sugar-binding activity and the mitogenic activity of galectin-1 purified from an avian sarcoma virus-transformed rat NRK cell line, 77N1. The purified galectin-1 (t-galectin-1) had potent mitogenic activity in BALB3T3 cells, but no sugar-binding activity. Treatment of t-galectin-1 with 2-mercaptoethanol decreased its mitogenic activity, but resulted in the appearance of a sugar binding activity. Chemical modification of sulfhydryl groups in purified t-galectin-1 with [14C]-iodoacetamide suggested the presence of intramolecular disulfide bonds. MALDI-TOF mass spectrometric analysis of the native and reduced forms of the tryptic peptides from t-galectin-1 showed that t-galectin-1 has two intramolecular disulfide bonds (Cys2-Cys16 and Cys42-Cys60). These studies suggest that these intramolecular disulfide bonds of t-galectin-1 are essential for its mitogenic activity and that the different activities may be regulated by structural changes caused by intramolecular disulfide bond-breakage.