Molecular Basis and Consequences of the Cytochrome c-tRNA Interaction.
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ABSTRACT:
SUBMITTER: Liu C
PROVIDER: S-EPMC4858987 | biostudies-literature | 2016 May
REPOSITORIES: biostudies-literature
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Project description:Dihydrouridine (D) is a highly conserved modified base found in tRNAs from all domains of life. Dihydrouridine synthase (Dus) catalyzes the D formation of tRNA through reduction of uracil base with flavin mononucleotide (FMN) as a cofactor. Here, we report the crystal structures of Thermus thermophilus Dus (TthDus), which is responsible for D formation at positions 20 and 20a, in complex with tRNA and with a short fragment of tRNA (D-loop). Dus interacts extensively with the D-arm and recognizes the elbow region composed of the kissing loop interaction between T- and D-loops in tRNA, pulling U20 into the catalytic center for reduction. Although distortion of the D-loop structure was observed upon binding of Dus to tRNA, the canonical D-loop/T-loop interaction was maintained. These results were consistent with the observation that Dus preferentially recognizes modified rather than unmodified tRNAs, indicating that Dus introduces D20 by monitoring the complete L-shaped structure of tRNAs. In the active site, U20 is stacked on the isoalloxazine ring of FMN, and C5 of the U20 uracil ring is covalently cross linked to the thiol group of Cys93, implying a catalytic mechanism of D20 formation. In addition, the involvement of a cofactor molecule in uracil ring recognition was proposed. Based on a series of mutation analyses, we propose a molecular basis of tRNA recognition and D formation catalyzed by Dus.
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Project description:Pyrrolysine (Pyl), the 22nd natural amino acid, is genetically encoded by UAG and inserted into proteins by the unique suppressor tRNA(Pyl) (ref. 1). The Methanosarcinaceae produce Pyl and express Pyl-containing methyltransferases that allow growth on methylamines. Homologous methyltransferases and the Pyl biosynthetic and coding machinery are also found in two bacterial species. Pyl coding is maintained by pyrrolysyl-tRNA synthetase (PylRS), which catalyses the formation of Pyl-tRNA(Pyl) (refs 4, 5). Pyl is not a recent addition to the genetic code. PylRS was already present in the last universal common ancestor; it then persisted in organisms that utilize methylamines as energy sources. Recent protein engineering efforts added non-canonical amino acids to the genetic code. This technology relies on the directed evolution of an 'orthogonal' tRNA synthetase-tRNA pair in which an engineered aminoacyl-tRNA synthetase (aaRS) specifically and exclusively acylates the orthogonal tRNA with a non-canonical amino acid. For Pyl the natural evolutionary process developed such a system some 3 billion years ago. When transformed into Escherichia coli, Methanosarcina barkeri PylRS and tRNA(Pyl) function as an orthogonal pair in vivo. Here we show that Desulfitobacterium hafniense PylRS-tRNA(Pyl) is an orthogonal pair in vitro and in vivo, and present the crystal structure of this orthogonal pair. The ancient emergence of PylRS-tRNA(Pyl) allowed the evolution of unique structural features in both the protein and the tRNA. These structural elements manifest an intricate, specialized aaRS-tRNA interaction surface that is highly distinct from those observed in any other known aaRS-tRNA complex; it is this general property that underlies the molecular basis of orthogonality.
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Project description:The highly conserved Elongator complex modifies transfer RNAs (tRNAs) in their wobble base position, thereby regulating protein synthesis and ensuring proteome stability. The precise mechanisms of tRNA recognition and its modification reaction remain elusive. Here, we show cryo-electron microscopy structures of the catalytic subcomplex of Elongator and its tRNA-bound state at resolutions of 3.3 and 4.4 Å. The structures resolve details of the catalytic site, including the substrate tRNA, the iron-sulfur cluster, and a SAM molecule, which are all validated by mutational analyses in vitro and in vivo. tRNA binding induces conformational rearrangements, which precisely position the targeted anticodon base in the active site. Our results provide the molecular basis for substrate recognition of Elongator, essential to understand its cellular function and role in neurodegenerative diseases and cancer.
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Project description:Background. Chronic renal failure is characterized by progressive renal scarring and accelerated cardiovascular disease. In animal models, this is thought to be due to non-dialyzable uremic toxins M-bM-^@M-^S small, protein-bound molecules normally secreted via Organic Anion Transporters (OATs) in the proximal renal tubule,rather than filtered at the glomerulus. The best studied of these is indoxyl sulfate (IS). Methods. We examined global gene expression responses in cultured normal human renal tubular cells incubated with control plasma (n=5) or pre- and post-dialysis uremic plasma (n=10). Results. GeneSpring analysis of microarrays revealed significantly altered expression of 2016 genes. The expression of 537 genes M-bM-^@M-^\normalizedM-bM-^@M-^] in post-dialysis plasma, suggesting removal of M-bM-^@M-^\low molecular weight uremic toxinsM-bM-^@M-^] by dialysis. The expression of the majority of dysregulated genes (1479) was not normalized in post-dialysis plasma. These likely represent the effects of substances not effectively removed by dialysis (M-bM-^@M-^\protein-bound uremic toxinsM-bM-^@M-^]). Addition of indoxyl sulfateto control plasma simulated most effects (81.1%) of uremic plasma, while the addition of probenecid, an OAT inhibitor, to uremic plasma reversed most changes in gene expression. Analysis of molecular programs with the Gene Set Enrichment Analysis and the DAVID database revealed patterns common to indoxyl sulfate-treated control plasma, pre-dialysis, and post-dialysis uremic plasma. These included increased cell cycle, pro-inflammatory, and pro-fibrotic molecular programs, particularly genes in the TGF-M-NM-2 pathway. Conclusion: These findings provide insight into the role of non-dialyzable, protein-bound uremic toxins in the pathogenesis of renal scarring and uremic vasculopathy. The GSEA patterns confirm that inflammatory and fibrotic programs are active. Transcriptomic remodeling in response to external stimulus RNA from non-immortalized cultured renal cortical cells incubated with plasma samples from 5 controls, 10 uremics pre-dialysis, 10 uremics post-dialysis, 5 controls with indoxyl sulfate added, 5 uremics pre-dialysis with probenecid added, 5 uremics post-dialysis with indoxyl sulfate added
2013-06-30 | E-GEOD-45709 | biostudies-arrayexpress
Project description:Cyclodipeptide synthases (CDPSs) catalyze the synthesis of various cyclodipeptides by using two aminoacyl-tRNA (aa-tRNA) substrates in a sequential mechanism. Here, we studied binding of phenylalanyl-tRNAPhe to the CDPS from Candidatus Glomeribacter gigasporarum (Cglo-CDPS) by gel filtration and electrophoretic mobility shift assay. We determined the crystal structure of the Cglo-CDPS:Phe-tRNAPhe complex to 5 Å resolution and further studied it in solution using small-angle X-ray scattering (SAXS). The data show that the major groove of the acceptor stem of the aa-tRNA interacts with the enzyme through the basic β2 and β7 strands of CDPSs belonging to the XYP subfamily. A bending of the CCA extremity enables the amino acid moiety to be positioned in the P1 pocket while the terminal A76 adenosine occupies the P2 pocket. Such a positioning indicates that the present structure illustrates the binding of the first aa-tRNA. In cells, CDPSs and the elongation factor EF-Tu share aminoacylated tRNAs as substrates. The present study shows that CDPSs and EF-Tu interact with opposite sides of tRNA. This may explain how CDPSs hijack aa-tRNAs from canonical ribosomal protein synthesis.
| S-EPMC7566563 | biostudies-literature
Project description:Background. Chronic renal failure is characterized by progressive renal scarring and accelerated cardiovascular disease. In animal models, this is thought to be due to non-dialyzable uremic toxins – small, protein-bound molecules normally secreted via Organic Anion Transporters (OATs) in the proximal renal tubule,rather than filtered at the glomerulus. The best studied of these is indoxyl sulfate (IS). Methods. We examined global gene expression responses in cultured normal human renal tubular cells incubated with control plasma (n=5) or pre- and post-dialysis uremic plasma (n=10). Results. GeneSpring analysis of microarrays revealed significantly altered expression of 2016 genes. The expression of 537 genes “normalized” in post-dialysis plasma, suggesting removal of “low molecular weight uremic toxins” by dialysis. The expression of the majority of dysregulated genes (1479) was not normalized in post-dialysis plasma. These likely represent the effects of substances not effectively removed by dialysis (“protein-bound uremic toxins”). Addition of indoxyl sulfateto control plasma simulated most effects (81.1%) of uremic plasma, while the addition of probenecid, an OAT inhibitor, to uremic plasma reversed most changes in gene expression. Analysis of molecular programs with the Gene Set Enrichment Analysis and the DAVID database revealed patterns common to indoxyl sulfate-treated control plasma, pre-dialysis, and post-dialysis uremic plasma. These included increased cell cycle, pro-inflammatory, and pro-fibrotic molecular programs, particularly genes in the TGF-β pathway. Conclusion: These findings provide insight into the role of non-dialyzable, protein-bound uremic toxins in the pathogenesis of renal scarring and uremic vasculopathy. The GSEA patterns confirm that inflammatory and fibrotic programs are active.
2013-06-30 | GSE45709 | GEO
Project description:METTL8 has recently been identified as the methyltransferase catalyzing 3-methylcytidine biogenesis at position 32 (m3C32) of mitochondrial tRNAs. METTL8 also potentially participates in mRNA methylation and R-loop biogenesis. How METTL8 plays multiple roles in distinct cell compartments and catalyzes mitochondrial tRNA m3C formation remain unclear. Here, we discovered that alternative mRNA splicing generated several isoforms of METTL8. One isoform (METTL8-Iso1) was targeted to mitochondria via an N-terminal pre-sequence, while another one (METTL8-Iso4) mainly localized to the nucleolus. METTL8-Iso1-mediated m3C32 modification of human mitochondrial tRNAThr (hmtRNAThr) was not reliant on t6A modification at A37 (t6A37), while that of hmtRNASer(UCN) critically depended on i6A modification at A37 (i6A37). We clarified the hmtRNAThr substrate recognition mechanism, which was obviously different from that of hmtRNASer(UCN), in terms of requiring a G35 determinant. Moreover, SARS2 (mitochondrial seryl-tRNA synthetase) interacted with METTL8-Iso1 in an RNA-independent manner and modestly accelerated m3C modification activity. We further elucidated how nonsubstrate tRNAs in human mitochondria were efficiently discriminated by METTL8-Iso1. In summary, our results established the expression pattern of METTL8, clarified the molecular basis for m3C32 modification by METTL8-Iso1 and provided the rationale for the involvement of METTL8 in tRNA modification, mRNA methylation or R-loop biogenesis.
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Project description:The linear ubiquitin (Ub) chain assembly complex (LUBAC) generates Met1-linked "linear" Ub chains that regulate the activation of the nuclear factor κB (NFκB) transcription factor and other processes. We recently discovered OTULIN as a deubiquitinase that specifically cleaves Met1-linked polyUb. Now, we show that OTULIN binds via a conserved PUB-interacting motif (PIM) to the PUB domain of the LUBAC component HOIP. Crystal structures and nuclear magnetic resonance experiments reveal the molecular basis for the high-affinity interaction and explain why OTULIN binds the HOIP PUB domain specifically. Analysis of LUBAC-induced NFκB signaling suggests that OTULIN needs to be present on LUBAC in order to restrict Met1-polyUb signaling. Moreover, LUBAC-OTULIN complex formation is regulated by OTULIN phosphorylation in the PIM. Phosphorylation of OTULIN prevents HOIP binding, whereas unphosphorylated OTULIN is part of the endogenous LUBAC complex. Our work exemplifies how coordination of ubiquitin assembly and disassembly activities in protein complexes regulates individual Ub linkage types.
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Project description:Variant interpretation remains a central challenge for precision medicine. Missense variants are particularly difficult to understand as they change only a single amino acid in a protein sequence yet can have large and varied effects on protein activity. Numerous tools have been developed to identify missense variants with putative disease consequences from protein sequence and structure. However, biological function arises through higher order interactions among proteins and molecules within cells. We therefore sought to capture information about the potential of missense mutations to perturb protein interaction networks by integrating protein structure and interaction data. We developed 16 network-based annotations for missense mutations that provide orthogonal information to features classically used to prioritize variants. We then evaluated them in the context of a proven machine-learning framework for variant effect prediction across multiple benchmark datasets to demonstrate their potential to improve variant classification. Interestingly, network features resulted in larger performance gains for classifying somatic mutations than for germline variants, possibly due to different constraints on what mutations are tolerated at the cellular versus organismal level. Our results suggest that modeling variant potential to perturb context-specific interactome networks is a fruitful strategy to advance in silico variant effect prediction.
| S-EPMC8873243 | biostudies-literature
Project description:Drug-drug interactions are a major cause of hospitalization and deaths related to drug use. A large fraction of these is due to inhibition of enzymes involved in drug metabolism and transport, particularly cytochrome P450 (P450) enzymes. Understanding basic mechanisms of enzyme inhibition is important, particularly in terms of reversibility and the use of the appropriate parameters. In addition to drug-drug interactions, issues have involved interactions of drugs with foods and natural products related to P450 enzymes. Predicting drug-drug interactions is a major effort in drug development in the pharmaceutical industry and regulatory agencies. With appropriate in vitro experiments, it is possible to stratify clinical drug-drug interaction studies. A better understanding of drug interactions and training of physicians and pharmacists has developed. Finally, some P450s have been the targets of drugs in some cancers and other disease states.
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