Taguchi H, Makino Y, Yoshida M
Tokyo Institute of Technology, Research Laboratory of Resources Utilization, Yokohama, Japan.
J Biol Chem. 1994 Mar 18;269(11):8529-34.
Chaperonin-60 is usually isolated as a tetradecameric form arranged as two stacked seven-member rings, and this structure has been considered to be required for promoting protein folding. However, monomeric chaperonin-60 (cpn60m), isolated from holo-chaperonin of Thermus thermophilus, and its proteolytic 50-kDa fragment, which lacks amino-terminal 78 amino acid residues, can interact with non-native rhodanese and lactate dehydrogenase, suppress formation of aggregates, and promote productive folding under the appropriate conditions. However, different from tetradecameric chaperonin-60, folding promoted by cpn60m and the 50-kDa fragment produces lower yields of active enzymes and does not require ATP or chaperonin-10. These effects are not due to transient reassembly of cpn60m into a tetradecamer during the reaction, since immobilized cpn60m and the 50-kDa fragment, both of which can not reassemble into a tetradecamer, can still promote protein folding. An excess amount of the 50-kDa fragment shows an inhibitory effect on MgATP-triggered holochaperonin-dependent folding, indicating the 50-kDa fragment and holo-chaperonin can interact with the same species of non-native proteins. Thus, cpn60m has an intrinsic activity as a molecular chaperone and amino-terminal region of cpn60 is dispensable for this activity.
伴侣蛋白60通常以十四聚体形式分离出来，其结构为两个堆叠的七聚体环，这种结构被认为是促进蛋白质折叠所必需的。然而，从嗜热栖热菌的全伴侣蛋白中分离出的单体伴侣蛋白60（cpn60m）及其缺乏氨基末端78个氨基酸残基的50 kDa蛋白水解片段，在适当条件下可以与非天然的硫氰酸酶和乳酸脱氢酶相互作用，抑制聚集体的形成，并促进有效的折叠。然而，与十四聚体伴侣蛋白60不同，cpn60m和50 kDa片段促进的折叠产生的活性酶产量较低，并且不需要ATP或伴侣蛋白10。这些效应不是由于cpn60m在反应过程中暂时重新组装成十四聚体，因为固定化的cpn60m和50 kDa片段都不能重新组装成十四聚体，但仍然可以促进蛋白质折叠。过量的50 kDa片段对MgATP触发的全伴侣蛋白依赖性折叠具有抑制作用，表明50 kDa片段和全伴侣蛋白可以与同一类非天然蛋白质相互作用。因此，cpn60m具有作为分子伴侣的内在活性，并且cpn60的氨基末端区域对于该活性是可有可无的。
