30S翻译启动复合体的结构
Angelita Simonetti1, Stefano Marzi, Alexander G Myasnikov
1Institute of Genetics and of Molecular and Cellular Biology, Department of Structural Biology and Genomics, Illkirch F-67404, France.
Nature
|September 2, 2008
概括
细菌翻译启动涉及fMet-tRNA的精确定位 (fMet) 在30S启动复合体 (30SIC) 中通过与启动因子IF1和IF2的相互作用. 这一结构洞察力澄清了70S启动复合体组装和GTP水解激活.
科学领域:
- 分子生物学分子生物学
- 结构生物学 结构生物学
- 生物化学 生物化学
背景情况:
- 翻译启动是蛋白质合成中的一个关键的,限制速度的步骤.
- 细菌启动包括通过启动因子 (IF1,IF2,IF3) 和fMet-tRNA ((fMet) 与30S核糖体子单元结合的选择mRNA启动位置和读取.
- 70S启动复合体 (70SIC) 的形成需要50S子单元的连接和启动因子的释放.
研究的目的:
- 想象30S启动复合体 (30SIC) 的结构,包括mRNA,fMet-tRNA (fMet),IF1和与GTP结合的IF2.
- 阐明稳定30SIC的精确相互作用及其在随后的70SIC组装中的作用.
- 了解50S子单元连接时GTP水解激活的机制.
主要方法:
- 低温电子显微镜 (cryo-EM) 是一种电子显微镜.
- 先进的颗粒分离技术可以分离颗粒.
- 三维统计分析三维统计分析
主要成果:
- 30SIC含有mRNA,fMet-tRNA (fMet),IF1和GTP结合的IF2的直接可视化.
- 确定了稳定30SIC的两个关键相互作用:tRNA解码干在30S基位和IF2碳基终端域与tRNA受体端.
- 证明IF2的GTP结合域面向50S子单元的GTP酶激活中心,解释了GTP水解激活.
结论:
- 在30SIC中fMet-tRNA ((fMet) 的精确定位对于稳定的复合体形成至关重要.
- 结构洞察力揭示了IF2如何调解70SIC组装所必需的相互作用.
- 这项研究为70SIC形成过程中GTP水解的快速激活提供了结构基础.
相关概念视频
Initiation of Translation
Initiating translation is complex because it involves multiple molecules. Initiator tRNA, ribosomal subunits, and eukaryotic initiation factors (eIFs) are all required to assemble on the initiation codon of mRNA. This process consists of several steps that are mediated by different eIFs.
First, the initiator tRNA must be selected from the pool of elongator tRNAs by eukaryotic initiation factor 2 (eIF2). The initiator tRNA (Met-tRNAi) has conserved sequence elements including modified bases at...
First, the initiator tRNA must be selected from the pool of elongator tRNAs by eukaryotic initiation factor 2 (eIF2). The initiator tRNA (Met-tRNAi) has conserved sequence elements including modified bases at...
Initiation of Translation
Initiating translation is complex because it involves multiple molecules. Initiator tRNA, ribosomal subunits, and eukaryotic initiation factors (eIFs) are all required to assemble on the initiation codon of mRNA. This process consists of several steps that are mediated by different eIFs.
First, the initiator tRNA must be selected from the pool of elongator tRNAs by eukaryotic initiation factor 2 (eIF2). The initiator tRNA (Met-tRNAi) has conserved sequence elements including modified bases at...
First, the initiator tRNA must be selected from the pool of elongator tRNAs by eukaryotic initiation factor 2 (eIF2). The initiator tRNA (Met-tRNAi) has conserved sequence elements including modified bases at...
Translation in Prokaryotes
Prokaryote translation is a complex, highly coordinated process that converts genetic information from mRNA into functional proteins. It involves three stages: initiation, elongation, and termination, each facilitated by specific molecular components.Initiation of TranslationThe process begins with the assembly of the ribosomal subunits and initiation factors on the mRNA. In bacteria, the 30S ribosomal subunit recognizes the Shine-Dalgarno sequence in the mRNA, a conserved region upstream of...
Termination of Translation
The large ribosomal subunit has several important structures essential to translation. These include the peptidyl transferase center (PTC) - which is the site where the peptide bond is formed - and a large, internal, water-filled tube through which the nascent polypeptide moves. This latter structure is called the Peptide Exit Tunnel, and it begins at the PTC and spans the body of the large ribosomal subunit. During translation, as the nascent polypeptide chain is synthesized, it passes through...
Leaky Scanning
During most eukaryotic translation processes, the small 40S ribosome subunit scans an mRNA from its 5' end until it encounters the first start AUG codon. The large 60S ribosomal subunit then joins the smaller one to initiate protein synthesis. The location of the translation initiation is largely determined by the nucleotides near the start codon as there may be multiple translation initiation sites present on the mRNA. Marilyn Kozak discovered that the sequence RCCAUGG (where R stands for...
Improving Translational Accuracy
Base complementarity between the three base pairs of mRNA codon and the tRNA anticodon is not a failsafe mechanism. Inaccuracies can range from a single mismatch to no correct base pairing at all. The free energy difference between the correct and nearly correct base pairs can be as small as 3 kcal/ mol. With complementarity being the only proofreading step, the estimated error frequency would be one wrong amino acid in every 100 amino acids incorporated. However, error frequencies observed in...


