Riccobono F, Fiani M L
Laboratorio di Biologia Cellulare, Istituto Superiore di Sanità, Rome, Italy.
Carbohydr Res. 1996 Mar 18;282(2):285-92. doi: 10.1016/0008-6215(95)00382-7.
The ricin A chain, the toxic subunit of ricin, consists of two forms which differ in sugar content. The major component A1 contains one high mannose chain while the minor component A2 contains an additional high mannose chain. Endocytosis of this toxin occurs in macrophages via the mannose receptor. To study the role of the sugar residues in ricin A chain cytotoxicity, we have purified the two forms by ion-exchange chromatography. The uptake of A1 and A2 by a macrophage cell line was concentration and time dependent. The total amount of A2 internalized was approximately twice the amount of A1, indicating a higher affinity of A2 for the mannose receptor. Ricin A2 was four times more toxic to macrophages than A1, in agreement with the higher affinity of A2 compared to the A1. These experiments suggest that the high mannose chains on the A chain promote mannose-receptor-mediated endocytosis by providing the initial binding to the cell surface. Once the toxin is accumulated inside the cell however, the carbohydrates do not seem to influence intracellular transport and/or translocation of the ricin A chain into the cytoplasm.
蓖麻毒素的毒性亚基蓖麻毒素A链由两种糖含量不同的形式组成。主要成分A1含有一条高甘露糖链，而次要成分A2含有一条额外的高甘露糖链。这种毒素通过甘露糖受体在巨噬细胞中发生内吞作用。为了研究糖残基在蓖麻毒素A链细胞毒性中的作用，我们通过离子交换色谱法纯化了这两种形式。巨噬细胞系对A1和A2的摄取呈浓度和时间依赖性。内化的A2总量约为A1的两倍，表明A2对甘露糖受体的亲和力更高。蓖麻毒素A2对巨噬细胞的毒性是A1的四倍，这与A2相对于A1具有更高的亲和力一致。这些实验表明，A链上的高甘露糖链通过提供与细胞表面的初始结合来促进甘露糖受体介导的内吞作用。然而，一旦毒素在细胞内积累，碳水化合物似乎不会影响蓖麻毒素A链在细胞内的运输和/或转运到细胞质中。
