30S翻訳開始複合体の構造
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
まとめ
バクテリアのトランスレーション開始には,fMet-tRNA (fMet) が30S開始複合体 (30SIC) の内部で,開始因子 IF1およびIF2との相互作用によって正確に位置づけられる. この構造的な洞察は,70S初期化複合体組立とGTP水解活性化を明確にします.
科学分野:
- 分子生物学は分子生物学である.
- 構造生物学 構造生物学とは
- バイオケミストリー バイオケミストリー
背景:
- トランスレーションの開始は,タンパク質合成において,速度を制限する重要なステップです.
- バクテリアのイニシエーションは,mRNAの開始部位と読み取りフレームをイニシエーション因子 (IF1,IF2,IF3) とfMet-tRNA (fMet) を30Sリボソームサブユニットに結合させることで選択する.
- 70S開始複合体 (70SIC) の形成には,50Sサブユニットの結合と開始因子の解放が必要です.
研究 の 目的:
- mRNA,fMet-tRNA (fMet),IF1およびGTP結合IF2を含む30Sイニシエーション複合体 (30SIC) の構造を視覚化するために.
- 30SICを安定させる正確な相互作用と,その後の70SIC組立におけるその役割を解明する.
- 50Sサブユニット結合時にGTP水解活性化のメカニズムを理解する.
主な方法:
- クリオ電子顕微鏡 (cryo-EM) とは
- 先進的な粒子分離技術が用いられている.
- 立体統計分析の3次元分析
主要な成果:
- mRNA,fMet-tRNA (fMet),IF1およびGTP結合IF2を含む30SICの直接視覚化
- 30SICを安定させる2つの重要な相互作用を特定した:30Sペプチジル部位のtRNA解読幹と,tRNA受容体末端とのIF2カルボキシ末端領域.
- IF2のGTP結合ドメインが50SサブユニットのGTP酵素活性化センターと向き合い,GTP水解活性化を説明することを実証した.
結論:
- 30SIC内のfMet-tRNA (fMet) の正確な位置づけは,安定した複合体の形成に極めて重要です.
- 構造的な洞察は,IF2が70SICの組み立てに不可欠な相互作用をどのように媒介するかを明らかにします.
- この研究は,70SIC形成中のGTP水解の急速な活性化のための構造的基礎を提供します.
関連する概念動画
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...


