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Tanzawa T, Kato K, Girodat D, Ose T, Kumakura Y, Wieden HJ, Uchiumi T, Tanaka I, Yao M. The C-terminal helix of ribosomal P stalk recognizes a hydrophobic groove of elongation factor 2 in a novel fashion. Nucleic Acids Res 2019; 46:3232-3244. [PMID: 29471537 PMCID: PMC5887453 DOI: 10.1093/nar/gky115] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Accepted: 02/09/2018] [Indexed: 01/17/2023] Open
Abstract
Archaea and eukaryotes have ribosomal P stalks composed of anchor protein P0 and aP1 homodimers (archaea) or P1•P2 heterodimers (eukaryotes). These P stalks recruit translational GTPases to the GTPase-associated center in ribosomes to provide energy during translation. The C-terminus of the P stalk is known to selectively recognize GTPases. Here we investigated the interaction between the P stalk and elongation factor 2 by determining the structures of Pyrococcus horikoshii EF-2 (PhoEF-2) in the Apo-form, GDP-form, GMPPCP-form (GTP-form), and GMPPCP-form bound with 11 C-terminal residues of P1 (P1C11). Helical structured P1C11 binds to a hydrophobic groove between domain G and subdomain G′ of PhoEF-2, where is completely different from that of aEF-1α in terms of both position and sequence, implying that such interaction characteristic may be requested by how GTPases perform their functions on the ribosome. Combining PhoEF-2 P1-binding assays with a structural comparison of current PhoEF-2 structures and molecular dynamics model of a P1C11-bound GDP form, the conformational changes of the P1C11-binding groove in each form suggest that in response to the translation process, the groove has three states: closed, open, and release for recruiting and releasing GTPases.
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Affiliation(s)
- Takehito Tanzawa
- Graduate School of Life Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
| | - Koji Kato
- Graduate School of Life Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.,Faculty of Advanced Life Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
| | - Dylan Girodat
- Alberta RNA Research and Training Institute, Department of Chemistry and Biochemistry, University of Lethbridge, Lethbridge AB T1K 3M4, Canada
| | - Toyoyuki Ose
- Graduate School of Life Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.,Faculty of Advanced Life Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
| | - Yuki Kumakura
- Graduate School of Life Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
| | - Hans-Joachim Wieden
- Alberta RNA Research and Training Institute, Department of Chemistry and Biochemistry, University of Lethbridge, Lethbridge AB T1K 3M4, Canada
| | - Toshio Uchiumi
- Department of Biology, Faculty of Science, Niigata University, 8050 Ikarashi 2-no-cho, Nishi-ku, Niigata 950-2181, Japan
| | - Isao Tanaka
- Faculty of Advanced Life Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
| | - Min Yao
- Graduate School of Life Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.,Faculty of Advanced Life Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
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2
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Girodat D, Mercier E, Gzyl KE, Wieden HJ. Elongation Factor Tu's Nucleotide Binding Is Governed by a Thermodynamic Landscape Unique among Bacterial Translation Factors. J Am Chem Soc 2019; 141:10236-10246. [PMID: 31058500 DOI: 10.1021/jacs.9b01522] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Molecular switches such as GTPases are powerful devices turning "on" or "off" biomolecular processes at the core of critical biological pathways. To develop molecular switches de novo, an intimate understanding of how they function is required. Here we investigate the thermodynamic parameters that define the nucleotide-dependent switch mechanism of elongation factor (EF) Tu as a prototypical molecular switch. EF-Tu alternates between GTP- and GDP-bound conformations during its functional cycle, representing the "on" and "off" states, respectively. We report for the first time that the activation barriers for nucleotide association are the same for both nucleotides, suggesting a guanosine nucleoside or ribose-first mechanism for nucleotide association. Additionally, molecular dynamics (MD) simulations indicate that enthalpic stabilization of GDP binding compared to GTP binding originates in the backbone hydrogen bonding network of EF-Tu. In contrast, binding of GTP to EF-Tu is entropically driven by the liberation of bound water during the GDP- to GTP-bound transition. GDP binding to the apo conformation of EF-Tu is both enthalpically and entropically favored, a feature unique among translational GTPases. This indicates that the apo conformation does not resemble the GDP-bound state. Finally, we show that antibiotics and single amino acid substitutions can be used to target specific structural elements in EF-Tu to redesign the thermodynamic landscape. These findings demonstrate how, through evolution, EF-Tu has fine-tuned the structural and dynamic features that define nucleotide binding, providing insight into how altering these properties could be exploited for protein engineering.
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Affiliation(s)
- Dylan Girodat
- Alberta RNA Research and Training Institute (ARRTI), Department of Chemistry and Biochemistry , University of Lethbridge , 4401 University Drive West , Lethbridge , Alberta T1K 3M4 , Canada
| | - Evan Mercier
- Alberta RNA Research and Training Institute (ARRTI), Department of Chemistry and Biochemistry , University of Lethbridge , 4401 University Drive West , Lethbridge , Alberta T1K 3M4 , Canada
| | - Katherine E Gzyl
- Alberta RNA Research and Training Institute (ARRTI), Department of Chemistry and Biochemistry , University of Lethbridge , 4401 University Drive West , Lethbridge , Alberta T1K 3M4 , Canada
| | - Hans-Joachim Wieden
- Alberta RNA Research and Training Institute (ARRTI), Department of Chemistry and Biochemistry , University of Lethbridge , 4401 University Drive West , Lethbridge , Alberta T1K 3M4 , Canada
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Sanbonmatsu KY. Large-scale simulations of nucleoprotein complexes: ribosomes, nucleosomes, chromatin, chromosomes and CRISPR. Curr Opin Struct Biol 2019; 55:104-113. [PMID: 31125796 DOI: 10.1016/j.sbi.2019.03.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2019] [Accepted: 03/01/2019] [Indexed: 12/11/2022]
Abstract
Recent advances in biotechnology such as Hi-C, CRISPR/Cas9 and ribosome display have placed nucleoprotein complexes at center stage. Understanding the structural dynamics of these complexes aids in optimizing protocols and interpreting data for these new technologies. The integration of simulation and experiment has helped advance mechanistic understanding of these systems. Coarse-grained simulations, reduced-description models, and explicit solvent molecular dynamics simulations yield useful complementary perspectives on nucleoprotein complex structural dynamics. When combined with Hi-C, cryo-EM, and single molecule measurements, these simulations integrate disparate forms of experimental data into a coherent mechanism.
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Trade-off and flexibility in the dynamic regulation of the cullin-RING ubiquitin ligase repertoire. PLoS Comput Biol 2017; 13:e1005869. [PMID: 29149173 PMCID: PMC5711038 DOI: 10.1371/journal.pcbi.1005869] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 12/01/2017] [Accepted: 11/02/2017] [Indexed: 11/19/2022] Open
Abstract
Cullin-RING ubiquitin ligases (CRLs) catalyze the ubiquitylation of substrates many of which are degraded by the 26S proteasome. Their modular architecture enables recognition of numerous substrates via exchangeable substrate receptors that competitively bind to a cullin scaffold with high affinity. Due to the plasticity of these interactions there is ongoing uncertainty how cells maintain a flexible CRL repertoire in view of changing substrate loads. Based on a series of in vivo and in vitro studies, different groups proposed that the exchange of substrate receptors is mediated by a protein exchange factor named Cand1. Here, we have performed mathematical modeling to provide a quantitative underpinning of this hypothesis. First we show that the exchange activity of Cand1 necessarily leads to a trade-off between high ligase activity and fast receptor exchange. Supported by measurements we argue that this trade-off yields an optimal Cand1 concentration in cells where the time scale for substrate degradation becomes minimal. In a second step we show through simulations that (i) substrates bias the CRL repertoire leading to preferential assembly of ligases for which substrates are available and (ii) differences in binding affinities or substrate receptor abundances create a temporal hierarchy for the degradation of substrates. Finally, we compare the Cand1-mediated exchange cycle with an alternative architecture lacking Cand1 which indicates superiority of a system with exchange factor if substrate receptors bind substrates and the cullin scaffold in a random order. Together, our results provide general constraints for the operating regimes of molecular exchange systems and suggest that Cand1 endows the CRL network with the properties of an “on demand” system allowing cells to dynamically adjust their CRL repertoire to fluctuating substrate abundances. Cullin-RING ubiquitin ligases (CRLs) are multisubunit protein complexes where exchangeable substrate receptors (SRs) assemble on a cullin scaffold to mediate ubiquitylation and subsequent degradation of a large variety of substrates. In humans there are hundreds of different CRLs having potentially thousands of substrates. Due to the high affinity of cullin-SR interactions, it has long been a mystery how cells would maintain flexibility to sample the entire SR repertoire in order to match fluctuating substrate loads. Recent experiments indicate that the exchange of different SRs is mediated by a novel protein exchange factor (Cand1). However, the proposed biochemical function of Cand1 as a promoter of CRL activity remained difficult to reconcile with previous reports of Cand1 acting as an inhibitor of CRL activity in vitro. Here we show that these two findings are not contradictory, but that the exchange activity of Cand1 necessarily leads to a trade-off between high ligase activity and fast receptor exchange which leads us to predict an optimal Cand1 concentration and a temporal hierarchy for substrate degradation. Our results support the view that Cand1 endows the CRL network with the flexibility of an “on demand” system where relative CRL abundances are dictated by substrate availability.
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5
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Tetracycline does not directly inhibit the function of bacterial elongation factor Tu. PLoS One 2017; 12:e0178523. [PMID: 28552981 PMCID: PMC5446176 DOI: 10.1371/journal.pone.0178523] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2017] [Accepted: 05/15/2017] [Indexed: 12/02/2022] Open
Abstract
Understanding the molecular mechanism of antibiotics that are currently in use is important for the development of new antimicrobials. The tetracyclines, discovered in the 1940s, are a well-established class of antibiotics that still have a role in treating microbial infections in humans. It is generally accepted that the main target of their action is the ribosome. The estimated affinity for tetracycline binding to the ribosome is relatively low compared to the actual potency of the drug in vivo. Therefore, additional inhibitory effects of tetracycline on the translation machinery have been discussed. Structural evidence suggests that tetracycline inhibits the function of the essential bacterial GTPase Elongation Factor (EF)-Tu through interaction with the bound nucleotide. Based on this, tetracycline has been predicted to impede the nucleotide-binding properties of EF-Tu. However, detailed kinetic studies addressing the effect of tetracycline on nucleotide binding have been prevented by the fluorescence properties of the antibiotic. Here, we report a fluorescence-based kinetic assay that minimizes the effect of tetracycline autofluorescence, enabling the detailed kinetic analysis of the nucleotide-binding properties of Escherichia coli EF-Tu. Furthermore, using physiologically relevant conditions, we demonstrate that tetracycline does not affect EF-Tu’s intrinsic or ribosome-stimulated GTPase activity, nor the stability of the EF-Tu•GTP•Phe-tRNAPhe complex. We therefore provide clear evidence that tetracycline does not directly impede the function of EF-Tu.
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De Laurentiis EI, Mercier E, Wieden HJ. The C-terminal Helix of Pseudomonas aeruginosa Elongation Factor Ts Tunes EF-Tu Dynamics to Modulate Nucleotide Exchange. J Biol Chem 2016; 291:23136-23148. [PMID: 27624934 DOI: 10.1074/jbc.m116.740381] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2016] [Indexed: 11/06/2022] Open
Abstract
Little is known about the conservation of critical kinetic parameters and the mechanistic strategies of elongation factor (EF) Ts-catalyzed nucleotide exchange in EF-Tu in bacteria and particularly in clinically relevant pathogens. EF-Tu from the clinically relevant pathogen Pseudomonas aeruginosa shares over 84% sequence identity with the corresponding elongation factor from Escherichia coli Interestingly, the functionally closely linked EF-Ts only shares 55% sequence identity. To identify any differences in the nucleotide binding properties, as well as in the EF-Ts-mediated nucleotide exchange reaction, we performed a comparative rapid kinetics and mutagenesis analysis of the nucleotide exchange mechanism for both the E. coli and P. aeruginosa systems, identifying helix 13 of EF-Ts as a previously unnoticed regulatory element in the nucleotide exchange mechanism with species-specific elements. Our findings support the base side-first entry of the nucleotide into the binding pocket of the EF-Tu·EF-Ts binary complex, followed by displacement of helix 13 and rapid binding of the phosphate side of the nucleotide, ultimately leading to the release of EF-Ts.
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Affiliation(s)
- Evelina Ines De Laurentiis
- From the Department of Chemistry and Biochemistry, Alberta RNA Research and Training Institute, University of Lethbridge, Lethbridge, Alberta T1K 3M4, Canada
| | - Evan Mercier
- From the Department of Chemistry and Biochemistry, Alberta RNA Research and Training Institute, University of Lethbridge, Lethbridge, Alberta T1K 3M4, Canada
| | - Hans-Joachim Wieden
- From the Department of Chemistry and Biochemistry, Alberta RNA Research and Training Institute, University of Lethbridge, Lethbridge, Alberta T1K 3M4, Canada
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Billod JM, Saenz-Mendez P, Blomberg A, Eriksson LA. Structures, Properties, and Dynamics of Intermediates in eEF2-Diphthamide Biosynthesis. J Chem Inf Model 2016; 56:1776-86. [PMID: 27525663 DOI: 10.1021/acs.jcim.6b00223] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The eukaryotic translation Elongation Factor 2 (eEF2) is an essential enzyme in protein synthesis. eEF2 contains a unique modification of a histidine (His699 in yeast; HIS) into diphthamide (DTA), obtained via 3-amino-3-carboxypropyl (ACP) and diphthine (DTI) intermediates in the biosynthetic pathway. This essential and unique modification is also vulnerable, in that it can be efficiently targeted by NAD(+)-dependent ADP-ribosylase toxins, such as diphtheria toxin (DT). However, none of the intermediates in the biosynthesis path is equally vulnerable against the toxins. This study aims to address the different susceptibility of DTA and its precursors against bacterial toxins. We have herein undertaken a detailed in silico study of the structural features and dynamic motion of different His699 intermediates along the diphthamide synthesis pathway (HIS, ACP, DTI, DTA). The study points out that DTA forms a strong hydrogen bond with an asparagine which might explain the ADP-ribosylation mechanism caused by the diphtheria toxin (DT). Finally, in silico mutagenesis studies were performed on the DTA modified protein, in order to hamper the formation of such a hydrogen bond. The results indicate that the mutant structure might in fact be less susceptible to attack by DT and thereby behave similarly to DTI in this respect.
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Affiliation(s)
- Jean-Marc Billod
- Department of Chemical and Physical Biology, Center for Biological Research, CIB-CSIC , 28040 Madrid, Spain
| | - Patricia Saenz-Mendez
- Computational Chemistry and Biology Group, Facultad de Química, Universidad de la República , 11800 Montevideo, Uruguay
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Mercier E, Girodat D, Wieden HJ. A conserved P-loop anchor limits the structural dynamics that mediate nucleotide dissociation in EF-Tu. Sci Rep 2015; 5:7677. [PMID: 25566871 PMCID: PMC4286738 DOI: 10.1038/srep07677] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2014] [Accepted: 12/05/2014] [Indexed: 01/11/2023] Open
Abstract
The phosphate-binding loop (P-loop) is a conserved sequence motif found in mononucleotide-binding proteins. Little is known about the structural dynamics of this region and its contribution to the observed nucleotide binding properties. Understanding the underlying design principles is of great interest for biomolecular engineering applications. We have used rapid-kinetics measurements in vitro and molecular dynamics (MD) simulations in silico to investigate the relationship between GTP-binding properties and P-loop structural dynamics in the universally conserved Elongation Factor (EF) Tu. Analysis of wild type EF-Tu and variants with substitutions at positions in or adjacent to the P-loop revealed a correlation between P-loop flexibility and the entropy of activation for GTP dissociation. The same variants demonstrate more backbone flexibility in two N-terminal amino acids of the P-loop during force-induced EF-Tu · GTP dissociation in Steered Molecular Dynamics simulations. Amino acids Gly18 and His19 are involved in stabilizing the P-loop backbone via interactions with the adjacent helix C. We propose that these P-loop/helix C interactions function as a conserved P-loop anchoring module and identify the presence of P-loop anchors within several GTPases and ATPases suggesting their evolutionary conservation.
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Affiliation(s)
- Evan Mercier
- Alberta RNA Research and Training Institute, Department of Chemistry and Biochemistry, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada
| | - Dylan Girodat
- Alberta RNA Research and Training Institute, Department of Chemistry and Biochemistry, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada
| | - Hans-Joachim Wieden
- Alberta RNA Research and Training Institute, Department of Chemistry and Biochemistry, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada
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9
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Friedt J, Leavens FMV, Mercier E, Wieden HJ, Kothe U. An arginine-aspartate network in the active site of bacterial TruB is critical for catalyzing pseudouridine formation. Nucleic Acids Res 2014; 42:3857-70. [PMID: 24371284 PMCID: PMC3973310 DOI: 10.1093/nar/gkt1331] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2013] [Revised: 11/27/2013] [Accepted: 11/30/2013] [Indexed: 11/12/2022] Open
Abstract
Pseudouridine synthases introduce the most common RNA modification and likely use the same catalytic mechanism. Besides a catalytic aspartate residue, the contributions of other residues for catalysis of pseudouridine formation are poorly understood. Here, we have tested the role of a conserved basic residue in the active site for catalysis using the bacterial pseudouridine synthase TruB targeting U55 in tRNAs. Substitution of arginine 181 with lysine results in a 2500-fold reduction of TruB's catalytic rate without affecting tRNA binding. Furthermore, we analyzed the function of a second-shell aspartate residue (D90) that is conserved in all TruB enzymes and interacts with C56 of tRNA. Site-directed mutagenesis, biochemical and kinetic studies reveal that this residue is not critical for substrate binding but influences catalysis significantly as replacement of D90 with glutamate or asparagine reduces the catalytic rate 30- and 50-fold, respectively. In agreement with molecular dynamics simulations of TruB wild type and TruB D90N, we propose an electrostatic network composed of the catalytic aspartate (D48), R181 and D90 that is important for catalysis by fine-tuning the D48-R181 interaction. Conserved, negatively charged residues similar to D90 are found in a number of pseudouridine synthases, suggesting that this might be a general mechanism.
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Affiliation(s)
- Jenna Friedt
- Department of Chemistry and Biochemistry, Alberta RNA Research and Training Institute, University of Lethbridge, Lethbridge AB T1K 3M4, Canada
| | - Fern M. V. Leavens
- Department of Chemistry and Biochemistry, Alberta RNA Research and Training Institute, University of Lethbridge, Lethbridge AB T1K 3M4, Canada
| | - Evan Mercier
- Department of Chemistry and Biochemistry, Alberta RNA Research and Training Institute, University of Lethbridge, Lethbridge AB T1K 3M4, Canada
| | - Hans-Joachim Wieden
- Department of Chemistry and Biochemistry, Alberta RNA Research and Training Institute, University of Lethbridge, Lethbridge AB T1K 3M4, Canada
| | - Ute Kothe
- Department of Chemistry and Biochemistry, Alberta RNA Research and Training Institute, University of Lethbridge, Lethbridge AB T1K 3M4, Canada
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Burnett BJ, Altman RB, Ferrao R, Alejo JL, Kaur N, Kanji J, Blanchard SC. Elongation factor Ts directly facilitates the formation and disassembly of the Escherichia coli elongation factor Tu·GTP·aminoacyl-tRNA ternary complex. J Biol Chem 2013; 288:13917-28. [PMID: 23539628 DOI: 10.1074/jbc.m113.460014] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
BACKGROUND Aminoacyl-tRNA (aa-tRNA) enters the ribosome in a ternary complex with the G-protein elongation factor Tu (EF-Tu) and GTP. RESULTS EF-Tu·GTP·aa-tRNA ternary complex formation and decay rates are accelerated in the presence of the nucleotide exchange factor elongation factor Ts (EF-Ts). CONCLUSION EF-Ts directly facilitates the formation and disassociation of ternary complex. SIGNIFICANCE This system demonstrates a novel function of EF-Ts. Aminoacyl-tRNA enters the translating ribosome in a ternary complex with elongation factor Tu (EF-Tu) and GTP. Here, we describe bulk steady state and pre-steady state fluorescence methods that enabled us to quantitatively explore the kinetic features of Escherichia coli ternary complex formation and decay. The data obtained suggest that both processes are controlled by a nucleotide-dependent, rate-determining conformational change in EF-Tu. Unexpectedly, we found that this conformational change is accelerated by elongation factor Ts (EF-Ts), the guanosine nucleotide exchange factor for EF-Tu. Notably, EF-Ts attenuates the affinity of EF-Tu for GTP and destabilizes ternary complex in the presence of non-hydrolyzable GTP analogs. These results suggest that EF-Ts serves an unanticipated role in the cell of actively regulating the abundance and stability of ternary complex in a manner that contributes to rapid and faithful protein synthesis.
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Affiliation(s)
- Benjamin J Burnett
- Departments of Physiology and Biophysics, Weill Cornell Medical College, New York, New York 10065, USA
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Burton B, Zimmermann MT, Jernigan RL, Wang Y. A computational investigation on the connection between dynamics properties of ribosomal proteins and ribosome assembly. PLoS Comput Biol 2012; 8:e1002530. [PMID: 22654657 PMCID: PMC3359968 DOI: 10.1371/journal.pcbi.1002530] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2011] [Accepted: 04/10/2012] [Indexed: 11/19/2022] Open
Abstract
Assembly of the ribosome from its protein and RNA constituents has been studied extensively over the past 50 years, and experimental evidence suggests that prokaryotic ribosomal proteins undergo conformational changes during assembly. However, to date, no studies have attempted to elucidate these conformational changes. The present work utilizes computational methods to analyze protein dynamics and to investigate the linkage between dynamics and binding of these proteins during the assembly of the ribosome. Ribosomal proteins are known to be positively charged and we find the percentage of positive residues in r-proteins to be about twice that of the average protein: Lys+Arg is 18.7% for E. coli and 21.2% for T. thermophilus. Also, positive residues constitute a large proportion of RNA contacting residues: 39% for E. coli and 46% for T. thermophilus. This affirms the known importance of charge-charge interactions in the assembly of the ribosome. We studied the dynamics of three primary proteins from E. coli and T. thermophilus 30S subunits that bind early in the assembly (S15, S17, and S20) with atomic molecular dynamic simulations, followed by a study of all r-proteins using elastic network models. Molecular dynamics simulations show that solvent-exposed proteins (S15 and S17) tend to adopt more stable solution conformations than an RNA-embedded protein (S20). We also find protein residues that contact the 16S rRNA are generally more mobile in comparison with the other residues. This is because there is a larger proportion of contacting residues located in flexible loop regions. By the use of elastic network models, which are computationally more efficient, we show that this trend holds for most of the 30S r-proteins. Ribosomes are complex cellular machines that synthesize new proteins in the cell. The accurate and efficient assembly of ribosomal proteins (r-proteins) and ribosomal RNA (rRNA) to form a functional ribosome is important for cell growth, metabolic reactions, and other cellular processes. Additionally, some antibacterial drugs are believed to target the bacterial ribosome during its construction. Hence, ribosomal assembly has been an active research topic for many years because understanding the assembly mechanisms can provide insight into protein/RNA recognitions important in many other cellular processes, as well as optimize the development of antibacterial therapeutics. Experimental studies thus far have provided still limited understanding about the assembly process. To further understand the assembly process, we have computationally studied the dynamic properties that r-proteins exhibit during assembly and the relationship between dynamics, physical properties, and binding propensity. We observe significant charged interactions between r-proteins and rRNA. We also detect a strong correlation between contact residues and their dynamic mobilities. Protein residues contacting with rRNA are observed to be more mobile in comparison with other residues. We also relate the location of the r-protein in the fully assembled ribosome to its susceptibility for large conformational changes prior to binding.
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Affiliation(s)
- Brittany Burton
- Department of Chemistry, The University of Memphis, Memphis, Tennessee, United States of America
| | - Michael T. Zimmermann
- Laurence H. Baker Center for Bioinformatics and Biological Statistics, Department of Biochemistry, Biophysics and Molecular Biology, Bioinformatics and Computational Biology Graduate Program, Iowa State University, Ames, Iowa, United States of America
| | - Robert L. Jernigan
- Laurence H. Baker Center for Bioinformatics and Biological Statistics, Department of Biochemistry, Biophysics and Molecular Biology, Bioinformatics and Computational Biology Graduate Program, Iowa State University, Ames, Iowa, United States of America
- * E-mail: (RLJ); (YW)
| | - Yongmei Wang
- Department of Chemistry, The University of Memphis, Memphis, Tennessee, United States of America
- * E-mail: (RLJ); (YW)
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12
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Abstract
BACKGROUND The process of solutes entrapment during liposomes formation is interesting for the investigation of the relationship between the formation of compartments and the distribution of molecules inside them; a relevant issue in the studies of the origin of life. Theoretically, when no interactions are supposed among the chemical species to be entrapped, the entrapment is described by a standard Poisson process. But very recent experimental findings show that, for small liposomes (100 nm diameter), the distribution of entrapped molecules is best described by a power-law function. This is of a great importance, as the two random processes give rise to two completely different scenarios. Here we present an in silico stochastic simulation of the encapsulation of a cell-free molecular translation system (the PURE system), obtained following two different entrapment models: a pure Poisson process, and a power-law. The protein synthesis inside the liposomes has been studied in both cases, with the aim to highlight experimental observables that could be measured to assess which model gives a better representation of the real process. RESULTS Firstly, a minimal model for in vitro protein synthesis, based on the PURE system molecular composition, has been formalized. Then, we have designed a reliable experimental simulation where stochastic factors affect the reaction course inside the compartment. To this end, 24 solutes, which represent the PURE system components, have been stochastically distributed among vesicles by following either a Poisson or a power-law distribution. The course of the protein synthesis within each vesicle has been consequently calculated, as a function of vesicle size. Our study can predict translation yield in a population of small liposomes down to the attoliter (10(-18) L) range. Our results show that the efficiency of protein synthesis peaks at approximately 3 · 10(-16) L (840 nm diam.) with a Poisson distribution of solutes, while a relative optimum is found at around 10(-17) L (275 nm diam.) for the power-law statistics. CONCLUSIONS Our simulation clearly shows that the wet-lab measurement of an effective protein synthesis at smaller volumes than 10(-17) L would rule out, according to our models, a Poisson distribution of solutes.
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13
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Sanbonmatsu KY. Computational studies of molecular machines: the ribosome. Curr Opin Struct Biol 2012; 22:168-74. [PMID: 22336622 DOI: 10.1016/j.sbi.2012.01.008] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2011] [Revised: 01/19/2012] [Accepted: 01/19/2012] [Indexed: 01/22/2023]
Abstract
The past decade has produced an avalanche of experimental data on the structure and dynamics of the ribosome. Groundbreaking studies in structural biology and kinetics have placed important constraints on ribosome structural dynamics. However, a gulf remains between static structures and time dependent data. In particular, X-ray crystallography and cryo-EM studies produce static models of the ribosome in various states, but lack dynamic information. Single molecule studies produce information on the rates of transitions between these states but do not have high-resolution spatial information. Computational studies have aided in bridging this gap by providing atomic resolution simulations of structural fluctuations and transitions between configurations.
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