Département de Biologie et de Génomique Structurales, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Université de Strasbourg, Illkirch 67400, France.
FEBS Lett. 2013 Jun 27;587(13):1848-57. doi: 10.1016/j.febslet.2013.05.009. Epub 2013 May 23.
Pioneer crystallographic studies of the isolated 30S ribosomal subunit provided the first structural insights into the decoding process. Recently, new crystallographic data on full 70S ribosomes with mRNA and tRNAs have shown that the formation of the tight decoding centre is ensured by conformational rearrangement of the 30S subunit (domain closure), which is identical for cognate or near-cognate tRNA. When a G·U forms at the first or second codon-anticodon positions (near-cognate tRNA), the ribosomal decoding centre forces the adoption of Watson-Crick G·C-like geometry rather than that of the expected Watson-Crick wobble pair. Energy expenditure for rarely occuring tautomeric base required for Watson-Crick G·C-like G·U pair or the repulsion energy due to steric clash within the mismatched base pair could constitute the only cause for efficient rejection of a near-cognate tRNA. Our data suggest that "geometrical mimicry" can explain how wrong aminoacyl-tRNAs with G·U pairs in the codon-anticodon helix forming base pairs with Watson-Crick geometry in the decoding center can be incorporated into the polypeptide chain.
先驱的孤立 30S 核糖体亚基的晶体学研究首次提供了对解码过程的结构见解。最近，关于带有 mRNA 和 tRNA 的完整 70S 核糖体的新晶体学数据表明，通过 30S 亚基的构象重排（结构域闭合）确保了紧密的解码中心的形成，对于同源或近同源 tRNA 都是如此。当第一个或第二个密码子-反密码子位置形成 G·U（近同源 tRNA）时，核糖体解码中心迫使采用 Watson-Crick G·C 样几何形状，而不是预期的 Watson-Crick 摆动对。为了形成 Watson-Crick G·C 样 G·U 对，很少发生的互变异构碱基所需的能量支出，或者由于错配碱基对内部的空间位阻而产生的排斥能，可能是有效拒绝近同源 tRNA 的唯一原因。我们的数据表明，“几何模拟”可以解释为什么在密码子-反密码子螺旋中形成 G·U 对的错误氨酰-tRNA 可以与解码中心中的 Watson-Crick 几何形状形成碱基对，并被掺入多肽链中。
