RESUMEN
Angiogenin, an RNase-A-family protein, promotes angiogenesis and has been implicated in cancer, neurodegenerative diseases and epigenetic inheritance1-10. After activation during cellular stress, angiogenin cleaves tRNAs at the anticodon loop, resulting in translation repression11-15. However, the catalytic activity of isolated angiogenin is very low, and the mechanisms of the enzyme activation and tRNA specificity have remained a puzzle3,16-23. Here we identify these mechanisms using biochemical assays and cryogenic electron microscopy (cryo-EM). Our study reveals that the cytosolic ribosome is the activator of angiogenin. A cryo-EM structure features angiogenin bound in the A site of the 80S ribosome. The C-terminal tail of angiogenin is rearranged by interactions with the ribosome to activate the RNase catalytic centre, making the enzyme several orders of magnitude more efficient in tRNA cleavage. Additional 80S-angiogenin structures capture how tRNA substrate is directed by the ribosome into angiogenin's active site, demonstrating that the ribosome acts as the specificity factor. Our findings therefore suggest that angiogenin is activated by ribosomes with a vacant A site, the abundance of which increases during cellular stress24-27. These results may facilitate the development of therapeutics to treat cancer and neurodegenerative diseases.
Asunto(s)
Microscopía por Crioelectrón , Ribonucleasa Pancreática , Ribosomas , Humanos , Anticodón/química , Anticodón/genética , Anticodón/metabolismo , Anticodón/ultraestructura , Dominio Catalítico , Citosol/metabolismo , Activación Enzimática , Modelos Moleculares , Ribonucleasa Pancreática/química , Ribonucleasa Pancreática/metabolismo , Ribonucleasa Pancreática/ultraestructura , Ribosomas/metabolismo , Ribosomas/química , Ribosomas/ultraestructura , División del ARN , ARN de Transferencia/química , ARN de Transferencia/metabolismo , Especificidad por Sustrato , Sitios de Unión , Estrés FisiológicoRESUMEN
Ribosomal incorporation of ß-amino acids into nascent peptides is much less efficient than that of the canonical α-amino acids. To overcome this, we have engineered a tRNA chimera bearing T-stem of tRNAGlu and D-arm of tRNAPro1, referred to as tRNAPro1E2, which efficiently recruits EF-Tu and EF-P. Using tRNAPro1E2 indeed improved ß-amino acid incorporation. However, multiple/consecutive incorporations of ß-amino acids are still detrimentally poor. Here, we attempted fine-tuning of the anticodon arm of tRNAPro1E2 aiming at further enhancement of ß-amino acid incorporation. By screening various mutations introduced into tRNAPro1E2, C31G39/C28G42 mutation showed an approximately 3-fold enhancement of two consecutive incorporation of ß-homophenylglycine (ßPhg) at CCG codons. The use of this tRNA made it possible for the first time to elongate up to ten consecutive ßPhg's. Since the enhancement effect of anticodon arm mutations differs depending on the codon used for ß-amino acid incorporation, we optimized anticodon arm sequences for five codons (CCG, CAU, CAG, ACU and UGG). Combination of the five optimal tRNAs for these codons made it possible to introduce five different kinds of ß-amino acids and analogs simultaneously into model peptides, including a macrocyclic scaffold. This strategy would enable ribosomal synthesis of libraries of macrocyclic peptides containing multiple ß-amino acids.
Asunto(s)
Aminoácidos , Anticodón , Anticodón/genética , Anticodón/química , Aminoácidos/química , Aminoácidos/genética , ARN de Transferencia/genética , ARN de Transferencia/química , ARN de Transferencia/metabolismo , Mutación , Codón/genética , Ribosomas/metabolismo , Ribosomas/genética , Biosíntesis de Proteínas , ARN de Transferencia de Prolina/genética , ARN de Transferencia de Prolina/metabolismo , ARN de Transferencia de Prolina/química , Conformación de Ácido Nucleico , Factor Tu de Elongación Peptídica/genética , Factor Tu de Elongación Peptídica/metabolismo , Escherichia coli/genética , Escherichia coli/metabolismoRESUMEN
The ribosome brings 3'-aminoacyl-tRNA and 3'-peptidyl-tRNAs together to enable peptidyl transfer by binding them in two major ways. First, their anticodon loops are bound to mRNA, itself anchored at the ribosomal subunit interface, by contiguous anticodon:codon pairing augmented by interactions with the decoding center of the small ribosomal subunit. Second, their acceptor stems are bound by the peptidyl transferase center, which aligns the 3'-aminoacyl- and 3'-peptidyl-termini for optimal interaction of the nucleophilic amino group and electrophilic ester carbonyl group. Reasoning that intrinsic codon:anticodon binding might have been a major contributor to bringing tRNA 3'-termini into proximity at an early stage of ribosomal peptide synthesis, we wondered if primordial amino acids might have been assigned to those codons that bind the corresponding anticodon loops most tightly. By measuring the binding of anticodon stem loops to short oligonucleotides, we determined that family-box codon:anticodon pairings are typically tighter than split-box codon:anticodon pairings. Furthermore, we find that two family-box anticodon stem loops can tightly bind a pair of contiguous codons simultaneously, whereas two split-box anticodon stem loops cannot. The amino acids assigned to family boxes correspond to those accessible by what has been termed cyanosulfidic chemistry, supporting the contention that these limited amino acids might have been the first used in primordial coded peptide synthesis.
Asunto(s)
Aminoácidos , Anticodón , Codón , Anticodón/química , Anticodón/genética , Aminoácidos/química , Codón/química , Codón/genética , Ribosomas/metabolismo , Ribosomas/química , Sitios de Unión , Modelos MolecularesRESUMEN
The frequency of errors upon decoding of messenger RNA by the bacterial ribosome is low, with one misreading event per 1 × 104 codons. In the universal genetic code, the AUN codon box specifies two amino acids, isoleucine and methionine. In bacteria and archaea, decoding specificity of the AUA and AUG codons relies on the wobble avoidance strategy that requires modification of C34 in the anticodon loop of isoleucine transfer RNAIleCAU (tRNAIleCAU). Bacterial tRNAIleCAU with 2-lysylcytidine (lysidine) at the wobble position deciphers AUA while avoiding AUG. Here we report cryo-electron microscopy structures of the Escherichia coli 70S ribosome complexed with elongation factor thermo unstable (EF-Tu) and isoleucine-tRNAIleLAU in the process of decoding AUA and AUG. Lysidine in tRNAIleLAU excludes AUG by promoting the formation of an unusual Hoogsteen purine-pyrimidine nucleobase geometry at the third position of the codon, weakening the interactions with the mRNA and destabilizing the EF-Tu ternary complex. Our findings elucidate the molecular mechanism by which tRNAIleLAU specifically decodes AUA over AUG.
Asunto(s)
Microscopía por Crioelectrón , Escherichia coli , Modelos Moleculares , Factor Tu de Elongación Peptídica , ARN de Transferencia de Isoleucina , Ribosomas , Factor Tu de Elongación Peptídica/metabolismo , Factor Tu de Elongación Peptídica/química , Factor Tu de Elongación Peptídica/genética , Escherichia coli/metabolismo , Escherichia coli/genética , Ribosomas/metabolismo , Ribosomas/ultraestructura , Ribosomas/química , ARN de Transferencia de Isoleucina/metabolismo , ARN de Transferencia de Isoleucina/química , ARN de Transferencia de Isoleucina/genética , Codón/metabolismo , Codón/genética , Anticodón/química , Anticodón/metabolismo , Conformación de Ácido Nucleico , Isoleucina/metabolismo , Isoleucina/química , ARN Mensajero/metabolismo , ARN Mensajero/química , ARN Mensajero/genética , Lisina/análogos & derivados , Nucleósidos de PirimidinaRESUMEN
The anticodon modifications of transfer RNAs (tRNAs) finetune the codon recognition on the ribosome for accurate translation. Bacteria and archaea utilize the modified cytidines, lysidine (L) and agmatidine (agm2C), respectively, in the anticodon of tRNAIle to decipher AUA codon. L and agm2C contain long side chains with polar termini, but their functions remain elusive. Here we report the cryogenic electron microscopy structures of tRNAsIle recognizing the AUA codon on the ribosome. Both modifications interact with the third adenine of the codon via a unique C-A geometry. The side chains extend toward 3' direction of the mRNA, and the polar termini form hydrogen bonds with 2'-OH of the residue 3'-adjacent to the AUA codon. Biochemical analyses demonstrated that AUA decoding is facilitated by the additional interaction between the polar termini of the modified cytidines and 2'-OH of the fourth mRNA residue. We also visualized cyclic N6-threonylcarbamoyladenosine (ct6A), another tRNA modification, and revealed a molecular basis how ct6A contributes to efficient decoding.
Asunto(s)
Anticodón , Microscopía por Crioelectrón , ARN de Transferencia de Isoleucina , ARN de Transferencia de Isoleucina/química , ARN de Transferencia de Isoleucina/metabolismo , ARN de Transferencia de Isoleucina/genética , Anticodón/química , Anticodón/metabolismo , Ribosomas/metabolismo , Ribosomas/química , Conformación de Ácido Nucleico , Modelos Moleculares , Codón/genética , Lisina/metabolismo , Lisina/química , Lisina/análogos & derivados , Citidina/análogos & derivados , Citidina/química , Citidina/metabolismo , ARN de Transferencia/metabolismo , ARN de Transferencia/química , ARN de Transferencia/genética , Biosíntesis de Proteínas , Nucleósidos de PirimidinaRESUMEN
Rapid and accurate translation is essential in all organisms to produce properly folded and functional proteins. mRNA codons that define the protein-coding sequences are decoded by tRNAs on the ribosome in the aminoacyl (A) binding site. The mRNA codon and the tRNA anticodon interaction is extensively monitored by the ribosome to ensure accuracy in tRNA selection. While other polymerases that synthesize DNA and RNA can correct for misincorporations, the ribosome is unable to correct mistakes. Instead, when a misincorporation occurs, the mismatched tRNA-mRNA pair moves to the peptidyl (P) site and, from this location, causes a reduction in the fidelity at the A site, triggering post-peptidyl transfer quality control. This reduced fidelity allows for additional incorrect tRNAs to be accepted and for release factor 2 (RF2) to recognize sense codons, leading to hydrolysis of the aberrant peptide. Here, we present crystal structures of the ribosome containing a tRNALys in the P site with a Uâ¢U mismatch with the mRNA codon. We find that when the mismatch occurs in the second position of the P-site codon-anticodon interaction, the first nucleotide of the A-site codon flips from the mRNA path to engage highly conserved 16S rRNA nucleotide A1493 in the decoding center. We propose that this mRNA nucleotide mispositioning leads to reduced fidelity at the A site. Further, this state may provide an opportunity for RF2 to initiate premature termination before erroneous nascent chains disrupt the cellular proteome.
Asunto(s)
Anticodón , Codón , ARN Ribosómico , Ribosomas , Anticodón/química , Anticodón/genética , Anticodón/metabolismo , Codón/química , Codón/genética , Codón/metabolismo , Conformación de Ácido Nucleico , Nucleótidos/química , Nucleótidos/metabolismo , Biosíntesis de Proteínas , Ribosomas/química , Ribosomas/metabolismo , ARN Mensajero/química , ARN Mensajero/metabolismo , ARN de Transferencia/química , ARN de Transferencia/metabolismo , Disparidad de Par Base , Modelos Moleculares , ARN Ribosómico/química , ARN Ribosómico/metabolismoRESUMEN
Cognate tRNAs deliver specific amino acids to translating ribosomes according to the standard genetic code, and three codons with no cognate tRNAs serve as stop codons. Some protists have reassigned all stop codons as sense codons, neglecting this fundamental principle1-4. Here we analyse the in-frame stop codons in 7,259 predicted protein-coding genes of a previously undescribed trypanosomatid, Blastocrithidia nonstop. We reveal that in this species in-frame stop codons are underrepresented in genes expressed at high levels and that UAA serves as the only termination codon. Whereas new tRNAsGlu fully cognate to UAG and UAA evolved to reassign these stop codons, the UGA reassignment followed a different path through shortening the anticodon stem of tRNATrpCCA from five to four base pairs (bp). The canonical 5-bp tRNATrp recognizes UGG as dictated by the genetic code, whereas its shortened 4-bp variant incorporates tryptophan also into in-frame UGA. Mimicking this evolutionary twist by engineering both variants from B. nonstop, Trypanosoma brucei and Saccharomyces cerevisiae and expressing them in the last two species, we recorded a significantly higher readthrough for all 4-bp variants. Furthermore, a gene encoding B. nonstop release factor 1 acquired a mutation that specifically restricts UGA recognition, robustly potentiating the UGA reassignment. Virtually the same strategy has been adopted by the ciliate Condylostoma magnum. Hence, we describe a previously unknown, universal mechanism that has been exploited in unrelated eukaryotes with reassigned stop codons.
Asunto(s)
Anticodón , Codón de Terminación , Células Eucariotas , Código Genético , Mutación , Factores de Terminación de Péptidos , ARN de Transferencia , Anticodón/química , Anticodón/genética , Anticodón/metabolismo , Cilióforos/genética , Codón de Terminación/genética , Código Genético/genética , Factores de Terminación de Péptidos/genética , Factores de Terminación de Péptidos/metabolismo , ARN de Transferencia/genética , ARN de Transferencia/metabolismo , ARN de Transferencia de Triptófano/genética , Saccharomyces cerevisiae/genética , ARN de Transferencia de Ácido Glutámico/genética , Trypanosoma brucei brucei/genéticaRESUMEN
Modified nucleotides in tRNAs are important determinants of folding, structure and function. Here we identify METTL8 as a mitochondrial matrix protein and active RNA methyltransferase responsible for installing m3C32 in the human mitochondrial (mt-)tRNAThr and mt-tRNASer(UCN). METTL8 crosslinks to the anticodon stem loop (ASL) of many mt-tRNAs in cells, raising the question of how methylation target specificity is achieved. Dissection of mt-tRNA recognition elements revealed U34G35 and t6A37/(ms2)i6A37, present concomitantly only in the ASLs of the two substrate mt-tRNAs, as key determinants for METTL8-mediated methylation of C32. Several lines of evidence demonstrate the influence of U34, G35, and the m3C32 and t6A37/(ms2)i6A37 modifications in mt-tRNAThr/Ser(UCN) on the structure of these mt-tRNAs. Although mt-tRNAThr/Ser(UCN) lacking METTL8-mediated m3C32 are efficiently aminoacylated and associate with mitochondrial ribosomes, mitochondrial translation is mildly impaired by lack of METTL8. Together these results define the cellular targets of METTL8 and shed new light on the role of m3C32 within mt-tRNAs.
Asunto(s)
Anticodón/química , Metiltransferasas/genética , Mitocondrias/genética , ARN Mitocondrial/química , ARN de Transferencia de Serina/química , ARN de Transferencia de Treonina/química , Anticodón/metabolismo , Emparejamiento Base , Citosina/metabolismo , Regulación de la Expresión Génica , Células HEK293 , Humanos , Metilación , Metiltransferasas/metabolismo , Mitocondrias/metabolismo , Conformación de Ácido Nucleico , Unión Proteica , Biosíntesis de Proteínas , ARN Mitocondrial/genética , ARN Mitocondrial/metabolismo , ARN de Transferencia de Serina/genética , ARN de Transferencia de Serina/metabolismo , ARN de Transferencia de Treonina/genética , ARN de Transferencia de Treonina/metabolismo , Transducción de SeñalRESUMEN
Human mitochondrial transcripts contain messenger and ribosomal RNAs flanked by transfer RNAs (tRNAs), which are excised by mitochondrial RNase (mtRNase) P and Z to liberate all RNA species. In contrast to nuclear or bacterial RNase P, mtRNase P is not a ribozyme but comprises three protein subunits that carry out RNA cleavage and methylation by unknown mechanisms. Here, we present the cryo-EM structure of human mtRNase P bound to precursor tRNA, which reveals a unique mechanism of substrate recognition and processing. Subunits TRMT10C and SDR5C1 form a subcomplex that binds conserved mitochondrial tRNA elements, including the anticodon loop, and positions the tRNA for methylation. The endonuclease PRORP is recruited and activated through interactions with its PPR and nuclease domains to ensure precise pre-tRNA cleavage. The structure provides the molecular basis for the first step of RNA processing in human mitochondria.
Asunto(s)
3-Hidroxiacil-CoA Deshidrogenasas/química , Metiltransferasas/química , Precursores del ARN/metabolismo , Procesamiento Postranscripcional del ARN , Ribonucleasa P/química , 3-Hidroxiacil-CoA Deshidrogenasas/metabolismo , Anticodón/química , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/metabolismo , Proteínas Arqueales/química , Proteínas Arqueales/metabolismo , Microscopía por Crioelectrón , Humanos , Metilación , Metiltransferasas/genética , Metiltransferasas/metabolismo , Mitocondrias/enzimología , Modelos Moleculares , Mutación Missense , Conformación de Ácido Nucleico , Unión Proteica , Conformación Proteica , Mapeo de Interacción de Proteínas , ARN de Hongos/metabolismo , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Ribonucleasa P/metabolismo , Especificidad de la Especie , Relación Estructura-Actividad , Especificidad por SustratoRESUMEN
During protein synthesis on ribosome, tRNA recognizes its cognate codon of mRNA through base-pairing with the anticodon. The 5'-end nucleotide of the anticodon is capable of wobble base-pairing, offering a molecular basis for codon degeneracy. The wobble nucleotide is often targeted for post-transcriptional modification, which affects the specificity and fidelity of the decoding process. Flipping-out of a wobble nucleotide in the anticodon loop has been proposed to be necessary for modifying enzymes to access the target nucleotide, which has been captured in selective structures of protein-bound complexes. Meanwhile, all other structures of free or ribosome-bound tRNA display anticodon bases arranged in stacked conformation. We report the X-ray crystal structure of unbound tRNAVal1 to a 2.04 Å resolution showing two different conformational states of wobble uridine in the anticodon loop, one stacked on the neighboring base and the other swiveled out toward solvent. In addition, the structure reveals a rare magnesium ion coordination to the nitrogen atom of a nucleobase, which has been sampled very rarely among known structures of nucleic acids.
Asunto(s)
Anticodón/metabolismo , Biosíntesis de Proteínas , ARN Mensajero/metabolismo , ARN de Transferencia de Valina/metabolismo , Ribosomas/metabolismo , Anticodón/química , Anticodón/genética , Emparejamiento Base , Escherichia coli/genética , Escherichia coli/metabolismo , Metales/metabolismo , Modelos Moleculares , Conformación de Ácido Nucleico , ARN Mensajero/química , ARN Mensajero/genética , ARN de Transferencia de Valina/química , ARN de Transferencia de Valina/genética , Ribosomas/genéticaRESUMEN
Specific interaction between the start codon, 5'-AUG-3', and the anticodon, 5'-CAU-3', ensures accurate initiation of translation. Recent studies show that several near-cognate start codons (e.g. GUG and CUG) can play a role in initiating translation in eukaryotes. However, the mechanism allowing initiation through mismatched base-pairs at the ribosomal decoding site is still unclear at an atomic level. In this work, we propose an extended simulation-based method to evaluate free energy profiles, through computing the distance between each base-pair of the triplet interactions involved in recognition of start codons in eukaryotic translation pre-initiation complex. Our method provides not only the free energy penalty for mismatched start codons relative to the AUG start codon, but also the preferred pathways of transitions between bound and unbound states, which has not been described by previous studies. To verify the method, the binding dynamics of cognate (AUG) and near-cognate start codons (CUG and GUG) were simulated. Evaluated free energy profiles agree with experimentally observed changes in initiation frequencies from respective codons. This work proposes for the first time how a G:U mismatch at the first position of codon (GUG)-anticodon base-pairs destabilizes the accommodation in the initiating eukaryotic ribosome and how initiation at a CUG codon is nearly as strong as, or sometimes stronger than, that at a GUG codon. Our method is expected to be applied to study the affinity changes for various mismatched base-pairs.
Asunto(s)
Codón Iniciador/genética , Codón Iniciador/metabolismo , Iniciación de la Cadena Peptídica Traduccional , Anticodón/química , Anticodón/genética , Anticodón/metabolismo , Emparejamiento Base , Secuencia de Bases , Codón Iniciador/química , Biología Computacional , Células Eucariotas/metabolismo , Modelos Biológicos , Simulación de Dinámica Molecular , Conformación de Ácido Nucleico , ARN Mensajero/química , ARN Mensajero/genética , ARN Mensajero/metabolismo , Ribosomas/metabolismo , TermodinámicaRESUMEN
Biogenic polyamines are natural aliphatic polycations formed from amino acids by biochemical pathways that are highly conserved from bacteria to humans. Their cellular concentrations are carefully regulated and dysregulation causes severe cell growth defects. Polyamines have high affinity for nucleic acids and are known to interact with mRNA, tRNA and rRNA to stimulate the translational machinery, but the exact molecular mechanism(s) for this stimulus is still unknown. Here we exploit that Escherichia coli is viable in the absence of polyamines, including the universally conserved putrescine and spermidine. Using global macromolecule labelling approaches we find that ribosome efficiency is reduced by 50-70% in the absence of polyamines and this reduction is caused by slow translation elongation speed. The low efficiency causes rRNA and multiple tRNA species to be overproduced in the absence of polyamines, suggesting an impact on the feedback regulation of stable RNA transcription. Importantly, we find that polyamine deficiency affects both tRNA levels and tRNA modification patterns. Specifically, a large fraction of tRNAhis, tRNAtyr and tRNAasn lack the queuosine modification in the anticodon "wobble" base, which can be reversed by addition of polyamines to the growth medium. In conclusion, we demonstrate that polyamines are needed for modification of specific tRNA, possibly by facilitating the interaction with modification enzymes.
Asunto(s)
Anticodón/química , Escherichia coli/genética , Poliaminas/química , Escherichia coli/metabolismo , Retroalimentación Fisiológica , Conformación de Ácido Nucleico , Biosíntesis de Proteínas , ARN Bacteriano/química , ARN Ribosómico/química , ARN de Transferencia/químicaRESUMEN
Viruses commonly use specifically folded RNA elements that interact with both host and viral proteins to perform functions important for diverse viral processes. Examples are found at the 3' termini of certain positive-sense ssRNA virus genomes where they partially mimic tRNAs, including being aminoacylated by host cell enzymes. Valine-accepting tRNA-like structures (TLSVal) are an example that share some clear homology with canonical tRNAs but have several important structural differences. Although many examples of TLSVal have been identified, we lacked a full understanding of their structural diversity and phylogenetic distribution. To address this, we undertook an in-depth bioinformatic and biochemical investigation of these RNAs, guided by recent high-resolution structures of a TLSVal We cataloged many new examples in plant-infecting viruses but also in unrelated insect-specific viruses. Using biochemical and structural approaches, we verified the secondary structure of representative TLSVal substrates and tested their ability to be valylated, confirming previous observations of structural heterogeneity within this class. In a few cases, large stem-loop structures are inserted within variable regions located in an area of the TLS distal to known host cell factor binding sites. In addition, we identified one virus whose TLS has switched its anticodon away from valine, causing a loss of valylation activity; the implications of this remain unclear. These results refine our understanding of the structural and functional mechanistic details of tRNA mimicry and how this may be used in viral infection.
Asunto(s)
Variación Genética , Virus de Insectos/genética , Filogenia , Virus de Plantas/genética , ARN de Transferencia de Valina/química , ARN Viral/química , Anticodón/química , Anticodón/metabolismo , Secuencia de Bases , Sitios de Unión , Biología Computacional , Virus de Insectos/clasificación , Virus de Insectos/metabolismo , Modelos Moleculares , Imitación Molecular , Virus de Plantas/clasificación , Virus de Plantas/metabolismo , Pliegue del ARN , ARN de Transferencia de Valina/genética , ARN de Transferencia de Valina/metabolismo , ARN Viral/genética , ARN Viral/metabolismo , Homología de Secuencia de Ácido Nucleico , Valina/metabolismoRESUMEN
A recent crystal structure of a ribosome complex undergoing partial translocation in the absence of elongation factor EF-G showed disruption of codon-anticodon pairing and slippage of the reading frame by -1, directly implicating EF-G in preservation of the translational reading frame. Among mutations identified in a random screen for dominant-lethal mutations of EF-G were a cluster of six that map to the tip of domain IV, which has been shown to contact the codon-anticodon duplex in trapped translocation intermediates. In vitro synthesis of a full-length protein using these mutant EF-Gs revealed dramatically increased -1 frameshifting, providing new evidence for a role for domain IV of EF-G in maintaining the reading frame. These mutations also caused decreased rates of mRNA translocation and rotational movement of the head and body domains of the 30S ribosomal subunit during translocation. Our results are in general agreement with recent findings from Rodnina and coworkers based on in vitro translation of an oligopeptide using EF-Gs containing mutations at two positions in domain IV, who found an inverse correlation between the degree of frameshifting and rates of translocation. Four of our six mutations are substitutions at positions that interact with the translocating tRNA, in each case contacting the RNA backbone of the anticodon loop. We suggest that EF-G helps to preserve the translational reading frame by preventing uncoupled movement of the tRNA through these contacts; a further possibility is that these interactions may stabilize a conformation of the anticodon that favors base-pairing with its codon.
Asunto(s)
Escherichia coli/genética , Sistema de Lectura Ribosómico , Mutación , Extensión de la Cadena Peptídica de Translación , Factor G de Elongación Peptídica/genética , Ribosomas/genética , Anticodón/química , Anticodón/metabolismo , Sitios de Unión , Codón/química , Codón/metabolismo , Escherichia coli/metabolismo , Histidina/genética , Histidina/metabolismo , Oligopéptidos/genética , Oligopéptidos/metabolismo , Factor G de Elongación Peptídica/química , Factor G de Elongación Peptídica/metabolismo , Unión Proteica , Dominios Proteicos , Dominios y Motivos de Interacción de Proteínas , Estructura Secundaria de Proteína , ARN Mensajero , ARN de Transferencia , Sistemas de Lectura , Proteínas Recombinantes de Fusión/química , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Ribosomas/metabolismoRESUMEN
Colicin D is a plasmid-encoded bacteriocin that specifically cleaves tRNAArg of sensitive Escherichia coli cells. E. coli has four isoaccepting tRNAArgs; the cleavage occurs at the 3' end of anticodon-loop, leading to translation impairment in the sensitive cells. tRNAs form a common L-shaped structure and have many conserved nucleotides that limit tRNA identity elements. How colicin D selects tRNAArgs from the tRNA pool of sensitive E. coli cells is therefore intriguing. Here, we reveal the recognition mechanism of colicin D via biochemical analyses as well as structural modelling. Colicin D recognizes tRNAArgICG, the most abundant species of E. coli tRNAArgs, at its anticodon-loop and D-arm, and selects it as the most preferred substrate by distinguishing its anticodon-loop sequence from that of others. It has been assumed that translation impairment is caused by a decrease in intact tRNA molecules due to cleavage. However, we found that intracellular levels of intact tRNAArgICG do not determine the viability of sensitive cells after such cleavage; rather, an accumulation of cleaved ones does. Cleaved tRNAArgICG dominant-negatively impairs translation in vitro. Moreover, we revealed that EF-Tu, which is required for the delivery of tRNAs, does not compete with colicin D for binding tRNAArgICG, which is consistent with our structural model. Finally, elevation of cleaved tRNAArgICG level decreases the viability of sensitive cells. These results suggest that cleaved tRNAArgICG transiently occupies ribosomal A-site in an EF-Tu-dependent manner, leading to translation impairment. The strategy should also be applicable to other tRNA-targeting RNases, as they, too, recognize anticodon-loops.Abbreviations: mnm5U: 5-methylaminomethyluridine; mcm5s2U: 5-methoxycarbonylmethyl-2-thiouridine.
Asunto(s)
Bacteriocinas/química , Colicinas/química , Escherichia coli/metabolismo , Biosíntesis de Proteínas , ARN Bacteriano/química , ARN de Transferencia de Arginina/química , Ribosomas/metabolismo , Anticodón/química , Anticodón/genética , Anticodón/metabolismo , Bacteriocinas/genética , Bacteriocinas/metabolismo , Emparejamiento Base , Sitios de Unión , Colicinas/genética , Colicinas/metabolismo , Escherichia coli/genética , Regulación Bacteriana de la Expresión Génica , Simulación del Acoplamiento Molecular , Conformación de Ácido Nucleico , Factor Tu de Elongación Peptídica/genética , Factor Tu de Elongación Peptídica/metabolismo , Plásmidos/química , Plásmidos/metabolismo , Unión Proteica , Conformación Proteica en Hélice alfa , Conformación Proteica en Lámina beta , Dominios y Motivos de Interacción de Proteínas , ARN Bacteriano/genética , ARN Bacteriano/metabolismo , ARN de Transferencia de Arginina/genética , ARN de Transferencia de Arginina/metabolismo , Ribosomas/genética , Especificidad por Sustrato , Tiouridina/análogos & derivados , Tiouridina/metabolismo , Uridina/análogos & derivados , Uridina/metabolismoRESUMEN
Transfer RNA (tRNA) is the most diversely modified RNA. Although the strictly conserved purine position 37 in the anticodon stem-loop undergoes modifications that are phylogenetically distributed, we do not yet fully understand the roles of these modifications. Therefore, molecular dynamics simulations are used to provide molecular-level details for how such modifications impact the structure and function of tRNA. A focus is placed on three hypermodified base families that include the parent i6A, t6A, and yW modifications, as well as derivatives. Our data reveal that the hypermodifications exhibit significant conformational flexibility in tRNA, which can be modulated by additional chemical functionalization. Although the overall structure of the tRNA anticodon stem remains intact regardless of the modification considered, the anticodon loop must rearrange to accommodate the bulky, dynamic hypermodifications, which includes changes in the nucleotide glycosidic and backbone conformations, and enhanced or completely new nucleobase-nucleobase interactions compared to unmodified tRNA or tRNA containing smaller (m1G) modifications at the 37th position. Importantly, the extent of the changes in the anticodon loop is influenced by the addition of small functional groups to parent modifications, implying each substituent can further fine-tune tRNA structure. Although the dominant conformation of the ASL is achieved in different ways for each modification, the molecular features of all modified tRNA drive the ASL domain to adopt the functional open-loop conformation. Importantly, the impact of the hypermodifications is preserved in different sequence contexts. These findings highlight the likely role of regulating mRNA structure and translation.
Asunto(s)
Adenosina/análogos & derivados , Anticodón/química , Escherichia coli/genética , Procesamiento Postranscripcional del ARN , ARN de Transferencia de Lisina/química , ARN de Transferencia de Fenilalanina/química , Adenosina/metabolismo , Anticodón/genética , Anticodón/metabolismo , Emparejamiento Base , Secuencia de Bases , Escherichia coli/metabolismo , Isopenteniladenosina/química , Isopenteniladenosina/metabolismo , Simulación de Dinámica Molecular , Conformación de Ácido Nucleico , Nucleósidos/química , Nucleósidos/metabolismo , ARN de Transferencia de Lisina/genética , ARN de Transferencia de Lisina/metabolismo , ARN de Transferencia de Fenilalanina/genética , ARN de Transferencia de Fenilalanina/metabolismoRESUMEN
Because ambient temperature affects biochemical reactions, organisms living in extreme temperature conditions adapt protein composition and structure to maintain biochemical functions. While it is not feasible to experimentally determine optimal growth temperature (OGT) for every known microbial species, organisms adapted to different temperatures have measurable differences in DNA, RNA and protein composition that allow OGT prediction from genome sequence alone. In this study, we built a 'tRNA thermometer' model using tRNA sequence to predict OGT. We used sequences from 100 archaea and 683 bacteria species as input to train two Convolutional Neural Network models. The first pairs individual tRNA sequences from different species to predict which comes from a more thermophilic organism, with accuracy ranging from 0.538 to 0.992. The second uses the complete set of tRNAs in a species to predict optimal growth temperature, achieving a maximum ${r^2}$ of 0.86; comparable with other prediction accuracies in the literature despite a significant reduction in the quantity of input data. This model improves on previous OGT prediction models by providing a model with minimum input data requirements, removing laborious feature extraction and data preprocessing steps and widening the scope of valid downstream analyses.
Asunto(s)
Adaptación Fisiológica/genética , Archaea/genética , Bacterias/genética , Genoma Arqueal , Genoma Bacteriano , ARN de Transferencia/química , Anticodón/química , Anticodón/metabolismo , Archaea/clasificación , Archaea/metabolismo , Bacterias/clasificación , Bacterias/metabolismo , Emparejamiento Base , Secuencia de Bases , Simulación por Computador , Modelos Genéticos , Redes Neurales de la Computación , Conformación de Ácido Nucleico , Filogenia , Estabilidad del ARN , ARN de Transferencia/genética , ARN de Transferencia/metabolismo , Temperatura , TermómetrosRESUMEN
Bacterial transfer RNAs (tRNAs) contain evolutionarily conserved sequences and modifications that ensure uniform binding to the ribosome and optimal translational accuracy despite differences in their aminoacyl attachments and anticodon nucleotide sequences. In the tRNA anticodon stem-loop, the anticodon sequence is correlated with a base pair in the anticodon loop (nucleotides 32 and 38) to tune the binding of each tRNA to the decoding center in the ribosome. Disruption of this correlation renders the ribosome unable to distinguish correct from incorrect tRNAs. The molecular basis for how these two tRNA features combine to ensure accurate decoding is unclear. Here, we solved structures of the bacterial ribosome containing either wild-type [Formula: see text] or [Formula: see text] containing a reversed 32-38 pair on cognate and near-cognate codons. Structures of wild-type [Formula: see text] bound to the ribosome reveal 23S ribosomal RNA (rRNA) nucleotide A1913 positional changes that are dependent on whether the codon-anticodon interaction is cognate or near cognate. Further, the 32-38 pair is destabilized in the context of a near-cognate codon-anticodon pair. Reversal of the pairing in [Formula: see text] ablates A1913 movement regardless of whether the interaction is cognate or near cognate. These results demonstrate that disrupting 32-38 and anticodon sequences alters interactions with the ribosome that directly contribute to misreading.
Asunto(s)
Biosíntesis de Proteínas/genética , ARN de Transferencia/química , ARN de Transferencia/genética , Anticodón/química , Anticodón/genética , Anticodón/metabolismo , Emparejamiento Base , Codón/genética , Codón/metabolismo , Cristalografía por Rayos X , Modelos Moleculares , Mutación , Conformación de Ácido Nucleico , ARN Bacteriano/química , ARN Bacteriano/genética , ARN Bacteriano/metabolismo , ARN Mensajero/genética , ARN Mensajero/metabolismo , ARN Ribosómico 23S/química , ARN Ribosómico 23S/genética , ARN Ribosómico 23S/metabolismo , ARN de Transferencia/metabolismo , Ribosomas/química , Ribosomas/metabolismo , Thermus thermophilus/genética , Thermus thermophilus/metabolismoRESUMEN
In the Elongator-dependent modification pathway, chemical modifications are introduced at the wobble uridines at position 34 in transfer RNAs (tRNAs), which serve to optimize codon translation rates. Here, we show that this three-step modification pathway exists in Dictyostelium discoideum, model of the evolutionary superfamily Amoebozoa. Not only are previously established modifications observable by mass spectrometry in strains with the most conserved genes of each step deleted, but also additional modifications are detected, indicating a certain plasticity of the pathway in the amoeba. Unlike described for yeast, D. discoideum allows for an unconditional deletion of the single tQCUG gene, as long as the Elongator-dependent modification pathway is intact. In gene deletion strains of the modification pathway, protein amounts are significantly reduced as shown by flow cytometry and Western blotting, using strains expressing different glutamine leader constructs fused to GFP. Most dramatic are these effects, when the tQCUG gene is deleted, or Elp3, the catalytic component of the Elongator complex is missing. In addition, Elp3 is the most strongly conserved protein of the modification pathway, as our phylogenetic analysis reveals. The implications of this observation are discussed with respect to the evolutionary age of the components acting in the Elongator-dependent modification pathway.
Asunto(s)
Dictyostelium/genética , ARN de Transferencia/metabolismo , Anticodón/química , Anticodón/metabolismo , Codón , Dictyostelium/metabolismo , Eliminación de Gen , Glutamina , Histona Acetiltransferasas/genética , Histona Acetiltransferasas/metabolismo , Mutación , Nucleósidos/química , Filogenia , Biosíntesis de Proteínas , Proteínas Protozoarias/clasificación , Proteínas Protozoarias/genética , Proteínas Protozoarias/metabolismo , Uridina/metabolismoRESUMEN
Queuosine (Q) is a conserved tRNA modification in bacteria and eukaryotes. Eukaryotic Q-tRNA modification occurs through replacing the guanine base with the scavenged metabolite queuine at the wobble position of tRNAs with G34U35N36 anticodon (Tyr, His, Asn, Asp) by the QTRT1/QTRT2 heterodimeric enzyme encoded in the genome. In humans, Q-modification in tRNATyr and tRNAAsp are further glycosylated with galactose and mannose, respectively. Although galactosyl-Q (galQ) and mannosyl-Q (manQ) can be measured by LC/MS approaches, the difficulty of detecting and quantifying these modifications with low sample inputs has hindered their biological investigations. Here we describe a simple acid denaturing gel and nonradioactive northern blot method to detect and quantify the fraction of galQ/manQ-modified tRNA using just microgram amounts of total RNA. Our method relies on the secondary amine group of galQ/manQ becoming positively charged to slow their migration in acid denaturing gels commonly used for tRNA charging studies. We apply this method to determine the Q and galQ/manQ modification kinetics in three human cells lines. For Q-modification, tRNAAsp is modified the fastest, followed by tRNAHis, tRNATyr, and tRNAAsn Compared to Q-modification, glycosylation occurs at a much slower rate for tRNAAsp, but at a similar rate for tRNATyr Our method enables easy access to study the function of these enigmatic tRNA modifications.