Lin S H, Chow L P, Chen Y L, Liaw Y C, Chen J K, Lin J Y
Institute of Biochemistry, College of Medicine, National Taiwan University, Taipei, Taiwan, Republic of China.
Eur J Biochem. 1996 Sep 15;240(3):564-9. doi: 10.1111/j.1432-1033.1996.0564h.x.
Abrin-a is a potent plant toxin that consists of A and B chains linked by a disulfide bond. The abrin-a A chain (AaTA) has N-glycosidase activity while the abrin-a B chain (AaTB) has galactose-binding activity. By partial tryptic digestion, the domain structure of abrin-a was investigated. Seven tryptic fragments with molecular masses greater than 3500 Da were isolated and characterized. One fragment, designated T-21 and consisting of 153 amino acid residues, contained the major part of the second domain of AaTB and, after cross-linking of T-21 with glutaraldehyde, the reaction product had the same level of hemagglutinating activity as native abrin. When the T-21 fragment was conjugated with AaTA, the conjugate inhibited protein biosynthesis in HeLa cells. This suggests that the T-21 fragment is able to bind specifically to cells; its conjugate facilitates membrane translocation of AaTA into cells and consequently inhibits protein biosynthesis. T-21, with a molecular mass less than AaTB, is therefore a potentially useful substance for the preparation of immunotoxins.
相思子毒素-a是一种强效植物毒素，由通过二硫键连接的A链和B链组成。相思子毒素-a的A链（AaTA）具有N-糖苷酶活性，而相思子毒素-a的B链（AaTB）具有半乳糖结合活性。通过胰蛋白酶部分消化，研究了相思子毒素-a的结构域结构。分离并鉴定了7个分子量大于3500 Da的胰蛋白酶片段。其中一个片段命名为T-21，由153个氨基酸残基组成，包含AaTB第二个结构域的主要部分，用戊二醛将T-21交联后，反应产物的血凝活性与天然相思子毒素相同。当T-21片段与AaTA偶联时，偶联物抑制HeLa细胞中的蛋白质生物合成。这表明T-21片段能够特异性结合细胞；其偶联物促进AaTA向细胞内的膜转位，从而抑制蛋白质生物合成。因此，分子量小于AaTB的T-21是制备免疫毒素的潜在有用物质。
