Saito Y, Ogura T, Kamio M, Sabe H, Uchiyama T, Honjo T
Department of Medical Chemistry, Kyoto University Faculty of Medicine, Japan.
Int Immunol. 1990;2(12):1167-77. doi: 10.1093/intimm/2.12.1167.
The interleukin 2 receptor (IL-2R) is composed of at least two polypeptides--a 55 kd protein (the L chain, p55, or alpha chain) and a 75 kd protein (the H chain, p75 or beta chain). The high-affinity binding of IL-2 results in the formation of a ternary complex consisting of IL-2 and the L and H chains. We found that the rate of high-affinity complex formation at 0 degrees C was about one-third of that at 37 degrees C. The reduction of high-affinity complex formation rate at lower temperatures correlates with the reduction of lateral diffusion within the membrane at lower temperatures. An anti-H chain antibody (2RB) inhibited the formation of the high-affinity complex at 0 degrees C but not at 37 degrees C. We studied the kinetics of the high-affinity complex formation at 37 degrees C after the preincubation of ATL-2 cells with the 2RB antibody and IL-2 at 0 degrees C. We found that the amount of IL-2.L complex formed initially at 0 degrees C was almost equivalent to the amount of high-affinity complex formed by subsequent incubation at 37 degrees C. These results suggest that the IL-2.L complex might be converted to the high-affinity IL-2R complex. Similar experiments using YTC3 cells, which express a smaller number of L chains, showed slower rates of high-affinity complex formation, in agreement with the affinity conversion/stepwise binding model.
白细胞介素2受体（IL-2R）至少由两种多肽组成——一种55kd的蛋白质（L链，p55或α链）和一种75kd的蛋白质（H链，p75或β链）。IL-2的高亲和力结合导致形成由IL-2以及L链和H链组成的三元复合物。我们发现，0℃时高亲和力复合物的形成速率约为37℃时的三分之一。较低温度下高亲和力复合物形成速率的降低与较低温度下膜内横向扩散的减少相关。一种抗H链抗体（2RB）在0℃时抑制高亲和力复合物的形成，但在37℃时不抑制。我们研究了ATL-2细胞在0℃与2RB抗体和IL-2预孵育后在37℃时高亲和力复合物形成的动力学。我们发现，0℃时最初形成的IL-2.L复合物的量几乎等同于随后在37℃孵育形成的高亲和力复合物的量。这些结果表明，IL-2.L复合物可能会转化为高亲和力的IL-2R复合物。使用表达较少数量L链的YTC3细胞进行的类似实验显示，高亲和力复合物的形成速率较慢，这与亲和力转换/逐步结合模型一致。
