Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1, Higashi, Tsukuba, Ibaraki 305-8566, Japan.
Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1, Higashi, Tsukuba, Ibaraki 305-8566, Japan.
Structure. 2015 May 5;23(5):830-842. doi: 10.1016/j.str.2015.03.013. Epub 2015 Apr 23.
The 3'-terminal CCA (C74C75A76-3') of tRNA is required for protein synthesis. In Aquifex aeolicus, the CCA-3' is synthesized by CC-adding and A-adding enzymes, although in most organisms, CCA is synthesized by a single CCA-adding enzyme. The mechanisms by which the A-adding enzyme adds only A76, but not C74C75, onto tRNA remained elusive. The complex structures of the enzyme with various tRNAs revealed the presence of a single tRNA binding site on the enzyme, with the enzyme measuring the acceptor-TΨC helix length of tRNA. The 3'-C75 of tRNA lacking A76 can reach the active site and the size and shape of the nucleotide binding pocket at the insertion stage are suitable for ATP. The 3'-C74 of tRNA lacking C75A76 cannot reach the active site, although CTP or ATP can bind the active pocket. Thus, the A-adding enzyme adds only A76, but not C74C75, onto tRNA.
tRNA 的 3'-末端 CCA（C74C75A76-3'）对于蛋白质合成是必需的。在水生栖热菌（Aquifex aeolicus）中，CCA-3'是由 CC 添加酶和 A 添加酶合成的，尽管在大多数生物体中，CCA 是由单个 CCA 添加酶合成的。A 添加酶仅将 A76 而不是 C74C75 添加到 tRNA 上的机制仍然难以捉摸。该酶与各种 tRNA 的复合物结构揭示了酶上存在单个 tRNA 结合位点，酶通过该位点测量 tRNA 的受体-TΨC 螺旋长度。缺乏 A76 的 tRNA 的 3'-C75 可以到达活性位点，并且在插入阶段核苷酸结合口袋的大小和形状适合 ATP。缺乏 C75A76 的 tRNA 的 3'-C74 无法到达活性位点，尽管 CTP 或 ATP 可以结合活性口袋。因此，A 添加酶仅将 A76 而不是 C74C75 添加到 tRNA 上。
