Nevskaya N, Tischenko S, Fedorov R, Al-Karadaghi S, Liljas A, Kraft A, Piendl W, Garber M, Nikonov S
Institute of Protein Research, Russian Academy of Sciences, Pushchino, 142292, Moscow Region, Russia.
Structure. 2000 Apr 15;8(4):363-71. doi: 10.1016/s0969-2126(00)00116-7.
L1 is an important primary rRNA-binding protein, as well as a translational repressor that binds mRNA. It was shown that L1 proteins from some bacteria and archaea are functionally interchangeable within the ribosome and in the repression of translation. The crystal structure of bacterial L1 from Thermus thermophilus (TthL1) has previously been determined.
We report here the first structure of a ribosomal protein from archaea, L1 from Methanococcus jannaschii (MjaL1). The overall shape of the two-domain molecule differs dramatically from that of its bacterial counterpart (TthL1) because of the different relative orientations of the domains. Two strictly conserved regions of the amino acid sequence, each belonging to one of the domains and positioned close to each other in the interdomain cavity of TthL1, are separated by about 25 A in MjaL1 owing to a significant opening of the structure. These regions are structurally highly conserved and are proposed to be the specific RNA-binding sites.
The unusually high RNA-binding affinity of MjaL1 might be explained by the exposure of its highly conserved regions. The open conformation of MjaL1 is strongly stabilized by nonconserved interdomain interactions and suggests that the closed conformations of L1 (as in TthL1) open upon RNA binding. Comparison of the two L1 protein structures reveals a high conformational variability of this ribosomal protein. Determination of the MjaL1 structure offers an additional variant for fitting the L1 protein into electron-density maps of the 50S ribosomal subunit.
L1是一种重要的初级核糖体RNA结合蛋白，也是一种结合mRNA的翻译抑制因子。研究表明，来自某些细菌和古菌的L1蛋白在核糖体功能以及翻译抑制方面具有功能互换性。嗜热栖热菌的细菌L1（TthL1）的晶体结构此前已被确定。
我们在此报告了首个来自古菌的核糖体蛋白——詹氏甲烷球菌的L1（MjaL1）的结构。由于结构域的相对方向不同，这个双结构域分子的整体形状与其细菌对应物（TthL1）有显著差异。氨基酸序列的两个严格保守区域，每个区域属于一个结构域，在TthL1的结构域间腔中彼此靠近，而在MjaL1中由于结构的显著开放，这两个区域相隔约25埃。这些区域在结构上高度保守，被认为是特定的RNA结合位点。
MjaL1异常高的RNA结合亲和力可能是由于其高度保守区域的暴露。MjaL1的开放构象通过非保守的结构域间相互作用得到强烈稳定，这表明L1的封闭构象（如TthL1中的）在RNA结合时会打开。两种L1蛋白结构的比较揭示了这种核糖体蛋白的高度构象变异性。MjaL1结构的确定为将L1蛋白拟合到50S核糖体亚基的电子密度图中提供了另一种变体。
