35,877 research outputs found
Translocation in action.
No full textRibosomes are macromolecular factories that translate the information encoded in messenger RNA (mRNA) into the amino acid sequence of proteins. Each time an amino acid has been transferred to the growing peptide chain, the mRNA and two transfer RNAs (tRNAs) move through the ribosome one codon at a time. This movement—called translocation—is promoted by elongation factor G (EF-G). Three papers in this issue, by Tourigny et al. (1), Pulk and Cate (2), and Zhou et al. (3), present high-resolution structures of translocation intermediates and provide insights into the underlying mechanism
The ribosome as a versatile catalyst: Reactions at the peptidyl transferase center.
No full textIn all contemporary organisms, the active site of the ribosome—the peptidyl transferase center—catalyzes two distinct reactions, peptide bond formation between peptidyl-tRNA and aminoacyl-tRNA as well as the hydrolysis of peptidyl-tRNA with the help of a release factor. However, when provided with appropriate substrates, ribosomes can also catalyze a broad range of other chemical reaction, which provides the basis for orthogonal translation and synthesis of alloproteins from unnatural building blocks. Advances in understanding the mechanisms of the two ubiquitous reactions, the peptide bond formation and peptide release, provide insights into the versatility of the active site of the ribosome. Release factors 1 and 2 and elongation factor P are auxiliary factors that augment the intrinsic catalytic activity of the ribosome in special cases
Visualizing the protein synthesis machinery: new focus on the translational GTPase elongation factor Tu.
No full textTranslation in prokaryotes.
No full textThis review summarizes our current understanding of translation in prokaryotes, focusing on the mechanistic and structural aspects of each phase of translation: initiation, elongation, termination, and ribosome recycling. The assembly of the initiation complex provides multiple checkpoints for messenger RNA (mRNA) and start-site selection. Correct codon–anticodon interaction during the decoding phase of elongation results in major conformational changes of the small ribosomal subunit and shapes the reaction pathway of guanosine triphosphate (GTP) hydrolysis. The ribosome orchestrates proton transfer during peptide bond formation, but requires the help of elongation factor P (EF-P) when two or more consecutive Pro residues are to be incorporated. Understanding the choreography of transfer RNA (tRNA) and mRNA movements during translocation helps to place the available structures of translocation intermediates onto the time axis of the reaction pathway. The nascent protein begins to fold cotranslationally, in the constrained space of the polypeptide exit tunnel of the ribosome. When a stop codon is reached at the end of the coding sequence, the ribosome, assisted by termination factors, hydrolyzes the ester bond of the peptidyl-tRNA, thereby releasing the nascent protein. Following termination, the ribosome is dissociated into subunits and recycled into another round of initiation. At each step of translation, the ribosome undergoes dynamic fluctuations between different conformation states. The aim of this article is to show the link between ribosome structure, dynamics, and function
The ribosome in action: Tuning of translational efficiency and protein folding.
No full textThe cellular proteome is shaped by the combined activities of the gene expression and quality control machineries. While transcription plays an undoubtedly important role, in recent years also translation emerged as a key step that defines the composition and quality of the proteome and the functional activity of proteins in the cell. Among the different post-transcriptional control mechanisms, translation initiation and elongation provide multiple checkpoints that can affect translational efficiency. A multitude of specific signals in mRNAs can determine the frequency of translation initiation, choice of the open reading frame, global and local elongation velocities, and the folding of the emerging protein. In addition to specific signatures in the mRNAs, also variations in the global pools of translation components, including ribosomes, tRNAs, mRNAs, and translation factors can alter translational efficiencies. The cellular outcomes of phenomena such as mRNA codon bias are sometimes difficult to understand due to the staggering complexity of co-variates that affect codon usage, translation, and protein folding. Here we summarize the experimental evidence on how the ribosome – together with the other components of the translational machinery – can alter translational efficiencies of mRNA at the initiation and elongation stages and how translation velocity affects protein folding. We seek to explain these findings in the context of mechanistic work on the ribosome. The results argue in favour of a new understanding of translation control as a hub that links mRNA homeostasis to production and quality control of proteins in the cell
Decoding and Recoding of mRNA Sequences by the Ribosome
No full textFaithful translation of messenger RNA (mRNA) into protein is essential to maintain protein homeostasis in the cell. Spontaneous translation errors are very rare due to stringent selection of cognate aminoacyl transfer RNAs (tRNAs) and the tight control of the mRNA reading frame by the ribosome. Recoding events, such as stop codon readthrough, frameshifting, and translational bypassing, reprogram the ribosome to make intentional mistakes and produce alternative proteins from the same mRNA. The hallmark of recoding is the change of ribosome dynamics. The signals for recoding are built into the mRNA, but their reading depends on the genetic makeup of the cell, resulting in cell-specific changes in expression programs. In this review, I discuss the mechanisms of canonical decoding and tRNA–mRNA translocation; describe alternative pathways leading to recoding; and identify the links among mRNA signals, ribosome dynamics, and recoding
Ten remarks on peptide bond formation on the ribosome
No full textPeptide-bond formation is the enzymatic activity of the ribosome. The catalytic site is made up of ribosomal RNA, indicating that the ribosome is a ribozyme. This review summarizes the recent progress in understanding the mechanism of peptide bond formation. The results of biochemical and kinetic experiments, mutagenesis studies and ribosome crystallography suggest that the approx. 107-fold rate enhancement of peptide bond formation by the ribosome is mainly due to substrate positioning within the active site, rather than to chemical catalysis.Peptide-bond formation is the enzymatic activity of the ribosome. The catalytic site is made up of ribosomal RNA, indicating that the ribosome is a ribozyme. This review summarizes the recent progress in understanding the mechanism of peptide bond formation. The results of biochemical and kinetic experiments, mutagenesis studies and ribosome crystallography suggest that the approx. 107-fold rate enhancement of peptide bond formation by the ribosome is mainly due to substrate positioning within the active site, rather than to chemical catalysis
Peptidyl-tRNA hydrolase as a key player in the liberation of truncated nascent chains from the ribosomal subunit
No full texthttp://dx.doi.org/10.13039/501100001659 German Research Foundatio
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