Molecular regulatory mechanism of cell surface garbohydrate expression and its pathology.

(1)分子内二硫键对TGF_< γ >2的肿瘤生长因子活性至关重要：TGF_< γ >2的氨基酸序列分析显示其为14Kda半乳糖苷结合蛋白（galectin-1）。然而，从大鼠肿瘤细胞中纯化的TGF_< γ >2没有糖结合活性。为了分析TGF_< γ bbb2和半乳糖凝集素-1在各活性上的差异，我们采用S-S桥化学裂解、模质谱和亲和层析等方法研究了TGF和半乳糖凝集素-1的分子内二硫键。多组证据表明，TGF活性需要TGF_<gamma>2分子内的S-S键，而凝集素活性是由TGF_<gamma>2分子内S-S键的断裂引起的，这可能是构象改变的结果。(2) GD3合成酶的分子克隆、表达及特异性：通过表达克隆策略获得了编码GD3合成酶的cDNA。克隆的GD3合成酶的底物特异性表明，该酶不仅能合成GD3，还能合成另一种唾液基转移酶SAT5所认为的GQ1b。这些结果表明该酶在中枢神经系统神经节苷脂表达调控中起关键作用。

(1) Intramolecular disulfide bonds are essential for the tumor growth factor activity of TGF_<gamma>2 : Amino acid sequence analysis of TGF_<gamma>2 revealed the identity 14Kda galactoside-binding protein (galectin-1) .The TGF_<gamma>2 purified from rat tumor cells, however, showed no sugar-binding activity.To analyze the difference in each activity between TGF_<gamma>2 and galectin-1, we studied the intramolecular disulfide bonds in TGF and galectin-1 by the several methods including chemical clevage of S-S bridge, MOLD-mass spectrometry and affinity chromatography.Several lines of evidences indicated that intramolecular S-S bonds in TFG_<gamma>2 is required for TGF activity and that the lectin activity is induced by thecleavage of S-S bonds in TGF_<gamma>2, possibly as a result of the conformational change.(2) Molecular cloning, expression and specificity of GD3 synthase : We obtained the cDNA encoding GD3 synthase by the expression cloning strategy.The substrate specificy of the cloned GD3 synthase showed that this enzyme synthesizes not only GD3, but GQ1b which was believed by the other sialyltransferase, SAT5.These results suggest this enzyme play a key role in the regulation of ganglioside expression in CNS.