1
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Wang J, Gisriel CJ, Reiss K, Huang HL, Armstrong WH, Brudvig GW, Batista VS. Heterogeneous Composition of Oxygen-Evolving Complexes in Crystal Structures of Dark-Adapted Photosystem II. Biochemistry 2021; 60:3374-3384. [PMID: 34714055 DOI: 10.1021/acs.biochem.1c00611] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Photosystem II (PSII) is a homodimeric protein complex that catalyzes water oxidation at the oxygen-evolving complex (OEC), a heterocubanoid calcium-tetramanganese cluster. Here, we analyze the omit electron density peaks of the OEC's metal ions in five X-ray free-electron laser PSII structures at resolutions between 2.15 and 1.95 Å. The omit peaks can be described by the total number of electrons and approximated by the variance of electron density distribution when the distributions are spherically symmetric. We show that the number of electrons of metal centers is different in the two OECs of PSII dimers, implying that the oxidation states and/or occupancies of individual metal ions are different in the two monomers. In either case, we find that the two OECs of dark-adapted PSII dimers in crystals are not fully synchronized in the S1 state. Differences in redox states of the OEC in PSII only partially account for the observation that the electron densities integrate to a smaller number of electrons than expected. Differences between the determined and expected relative electron numbers are much larger than the estimated errors, indicating heterogeneity in the OEC composition.
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Affiliation(s)
- Jimin Wang
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8114, United States
| | - Christopher J Gisriel
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Krystle Reiss
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Hao-Li Huang
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - William H Armstrong
- Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467, United States
| | - Gary W Brudvig
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8114, United States.,Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Victor S Batista
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
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2
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Chan CW, Badong D, Rajan R, Mondragón A. Crystal structures of an unmodified bacterial tRNA reveal intrinsic structural flexibility and plasticity as general properties of unbound tRNAs. RNA (NEW YORK, N.Y.) 2020; 26:278-289. [PMID: 31848215 PMCID: PMC7025506 DOI: 10.1261/rna.073478.119] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/27/2019] [Accepted: 12/12/2019] [Indexed: 06/10/2023]
Abstract
Ubiquitous across all domains of life, tRNAs constitute an essential component of cellular physiology, carry out an indispensable role in protein synthesis, and have been historically the subject of a wide range of biochemical and biophysical studies as prototypical folded RNA molecules. Although conformational flexibility is a well-established characteristic of tRNA structure, it is typically regarded as an adaptive property exhibited in response to an inducing event, such as the binding of a tRNA synthetase or the accommodation of an aminoacyl-tRNA into the ribosome. In this study, we present crystallographic data of a tRNA molecule to expand on this paradigm by showing that structural flexibility and plasticity are intrinsic properties of tRNAs, apparent even in the absence of other factors. Based on two closely related conformations observed within the same crystal, we posit that unbound tRNAs by themselves are flexible and dynamic molecules. Furthermore, we demonstrate that the formation of the T-loop conformation by the tRNA TΨC stem-loop, a well-characterized and classic RNA structural motif, is possible even in the absence of important interactions observed in fully folded tRNAs.
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Affiliation(s)
- Clarence W Chan
- Department of Molecular Biosciences, Northwestern University, Evanston, Illinois 60208-3500, USA
| | - Deanna Badong
- Department of Molecular Biosciences, Northwestern University, Evanston, Illinois 60208-3500, USA
| | - Rakhi Rajan
- Department of Molecular Biosciences, Northwestern University, Evanston, Illinois 60208-3500, USA
| | - Alfonso Mondragón
- Department of Molecular Biosciences, Northwestern University, Evanston, Illinois 60208-3500, USA
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3
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Williams AE, Thompson AL, Watkin DJ. The role of multiple observations in small-molecule single-crystal service X-ray structure determination. ACTA CRYSTALLOGRAPHICA SECTION B, STRUCTURAL SCIENCE, CRYSTAL ENGINEERING AND MATERIALS 2019; 75:657-673. [PMID: 32830722 DOI: 10.1107/s2052520619006681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Accepted: 05/09/2019] [Indexed: 06/11/2023]
Abstract
In order to gain a better understanding of how to improve the quality of small-molecule single-crystal X-ray diffraction data achievable in a finite time, a study was carried out to investigate the effect of varying the multiplicity, acquisition time, detector binning, maximum resolution and completeness. The results suggest that, unless there are strong arguments for a different strategy, a good routine procedure might be to optimize the conditions necessary to get the best data from single scans, and then choose a multiplicity of observations (MoO) to utilize the available time fully. Different strategies may be required if the crystal is highly absorbing, is larger than the incident beam, is enclosed in a capillary tube or is unusual in some other way. The signal-to-noise ratio should be used with care, as collecting data for longer or at higher multiplicity appears to give a systematic underestimate of the intensity uncertainties. Further, the results demonstrate that including poor-quality data in a refinement may degrade the result and, in the general case, the accidental omission of reflections has a very small impact on the refinement as long as they are omitted at random. Systematic omission of reflections needs a convincing procedural justification.
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Affiliation(s)
- Alice E Williams
- Chemical Crystallography, Chemistry Research Laboratory, Mansfield Road, Oxford OX1 3TA, England
| | - Amber L Thompson
- Chemical Crystallography, Chemistry Research Laboratory, Mansfield Road, Oxford OX1 3TA, England
| | - David J Watkin
- Chemical Crystallography, Chemistry Research Laboratory, Mansfield Road, Oxford OX1 3TA, England
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4
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Leonarski F, D'Ascenzo L, Auffinger P. Nucleobase carbonyl groups are poor Mg 2+ inner-sphere binders but excellent monovalent ion binders-a critical PDB survey. RNA (NEW YORK, N.Y.) 2019; 25:173-192. [PMID: 30409785 PMCID: PMC6348993 DOI: 10.1261/rna.068437.118] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2018] [Accepted: 10/16/2018] [Indexed: 05/04/2023]
Abstract
Precise knowledge of Mg2+ inner-sphere binding site properties is vital for understanding the structure and function of nucleic acid systems. Unfortunately, the PDB, which represents the main source of Mg2+ binding sites, contains a substantial number of assignment issues that blur our understanding of the functions of these ions. Here, following a previous study devoted to Mg2+ binding to nucleobase nitrogens, we surveyed nucleic acid X-ray structures from the PDB with resolutions ≤2.9 Å to classify the Mg2+ inner-sphere binding patterns to nucleotide carbonyl, ribose hydroxyl, cyclic ether, and phosphodiester oxygen atoms. From this classification, we derived a set of "prior-knowledge" nucleobase Mg2+ binding sites. We report that crystallographic examples of trustworthy nucleobase Mg2+ binding sites are fewer than expected since many of those are associated with misidentified Na+ or K+ We also emphasize that binding of Na+ and K+ to nucleic acids is much more frequent than anticipated. Overall, we provide evidence derived from X-ray structures that nucleobases are poor inner-sphere binders for Mg2+ but good binders for monovalent ions. Based on strict stereochemical criteria, we propose an extended set of guidelines designed to help in the assignment and validation of ions directly contacting nucleobase and ribose atoms. These guidelines should help in the interpretation of X-ray and cryo-EM solvent density maps. When borderline Mg2+ stereochemistry is observed, alternative placement of Na+, K+, or Ca2+ must be considered. We also critically examine the use of lanthanides (Yb3+, Tb3+) as Mg2+ substitutes in crystallography experiments.
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Affiliation(s)
- Filip Leonarski
- Swiss Light Source, Paul Scherrer Institut, Villigen PSI, 5232, Switzerland
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire du CNRS, Strasbourg, 67084, France
| | - Luigi D'Ascenzo
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire du CNRS, Strasbourg, 67084, France
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, California 92037, USA
| | - Pascal Auffinger
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire du CNRS, Strasbourg, 67084, France
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5
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Pechlaner M, Dominguez-Martin A, Sigel RKO. Influence of pH and Mg(ii) on the catalytic core domain 5 of a bacterial group II intron. Dalton Trans 2018; 46:3989-3995. [PMID: 28265619 DOI: 10.1039/c6dt04784j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
RNA molecules fold into complex structures that allow them to perform specific functions. To compensate the relative lack of diversity of functional groups within nucleotides, metal ions work as crucial co-factors. In addition, shifted pKas are observed in RNA, enabling acid-base reactions at ambient pH. The central catalytic domain 5 (D5) hairpin of the Azotobacter vinelandii group II intron undergoes both metal ion binding and pH dependence, presumably playing an important functional role in the ribozyme's reaction. By NMR spectroscopy we have here characterized the metal ion binding sites and affinities for the hairpin's internal G-A mismatch, bulge, and pentaloop. The influence of Mg(ii) and pH on the local conformation of the catalytically crucial region is also explored by fluorescence spectroscopy.
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Affiliation(s)
- M Pechlaner
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich, Switzerland.
| | - A Dominguez-Martin
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich, Switzerland.
| | - R K O Sigel
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich, Switzerland.
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6
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Watkins AM, Geniesse C, Kladwang W, Zakrevsky P, Jaeger L, Das R. Blind prediction of noncanonical RNA structure at atomic accuracy. SCIENCE ADVANCES 2018; 4:eaar5316. [PMID: 29806027 PMCID: PMC5969821 DOI: 10.1126/sciadv.aar5316] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2017] [Accepted: 04/17/2018] [Indexed: 05/26/2023]
Abstract
Prediction of RNA structure from nucleotide sequence remains an unsolved grand challenge of biochemistry and requires distinct concepts from protein structure prediction. Despite extensive algorithmic development in recent years, modeling of noncanonical base pairs of new RNA structural motifs has not been achieved in blind challenges. We report a stepwise Monte Carlo (SWM) method with a unique add-and-delete move set that enables predictions of noncanonical base pairs of complex RNA structures. A benchmark of 82 diverse motifs establishes the method's general ability to recover noncanonical pairs ab initio, including multistrand motifs that have been refractory to prior approaches. In a blind challenge, SWM models predicted nucleotide-resolution chemical mapping and compensatory mutagenesis experiments for three in vitro selected tetraloop/receptors with previously unsolved structures (C7.2, C7.10, and R1). As a final test, SWM blindly and correctly predicted all noncanonical pairs of a Zika virus double pseudoknot during a recent community-wide RNA-Puzzle. Stepwise structure formation, as encoded in the SWM method, enables modeling of noncanonical RNA structure in a variety of previously intractable problems.
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Affiliation(s)
- Andrew M. Watkins
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Caleb Geniesse
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA
- Biophysics Program, Stanford University, Stanford, CA 94305, USA
| | - Wipapat Kladwang
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Paul Zakrevsky
- Department of Chemistry and Biochemistry, Biomolecular Science and Engineering Program, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
| | - Luc Jaeger
- Department of Chemistry and Biochemistry, Biomolecular Science and Engineering Program, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
| | - Rhiju Das
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA
- Biophysics Program, Stanford University, Stanford, CA 94305, USA
- Department of Physics, Stanford University, Stanford, CA 94305, USA
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7
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Leonarski F, D'Ascenzo L, Auffinger P. Mg2+ ions: do they bind to nucleobase nitrogens? Nucleic Acids Res 2017; 45:987-1004. [PMID: 27923930 PMCID: PMC5314772 DOI: 10.1093/nar/gkw1175] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2016] [Revised: 11/10/2016] [Accepted: 11/14/2016] [Indexed: 01/28/2023] Open
Abstract
Given the many roles proposed for Mg2+ in nucleic acids, it is essential to accurately determine their binding modes. Here, we surveyed the PDB to classify Mg2+ inner-sphere binding patterns to nucleobase imine N1/N3/N7 atoms. Among those, purine N7 atoms are considered to be the best nucleobase binding sites for divalent metals. Further, Mg2+ coordination to N7 has been implied in several ribozyme catalytic mechanisms. We report that Mg2+ assigned near imine nitrogens derive mostly from poor interpretations of electron density patterns and are most often misidentified Na+, K+, NH4+ ions, water molecules or spurious density peaks. Consequently, apart from few documented exceptions, Mg2+ ions do not bind to N7 atoms. Without much of a surprise, Mn2+, Zn2+ and Cd2+, which have a higher affinity for nitrogens, may contact N7 atoms when present in crystallization buffers. In this respect, we describe for the first time a potential Zn2+ ribosomal binding site involving two purine N7 atoms. Further, we provide a set of guidelines to help in the assignment of Mg2+ in crystallographic, cryo-EM, NMR and model building practices and discuss implications of our findings related to ion substitution experiments.
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Affiliation(s)
- Filip Leonarski
- Université de Strasbourg, CNRS, Architecture et Réactivité de l'ARN, UPR9002, F-67000 Strasbourg, France
- Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
| | - Luigi D'Ascenzo
- Université de Strasbourg, CNRS, Architecture et Réactivité de l'ARN, UPR9002, F-67000 Strasbourg, France
| | - Pascal Auffinger
- Université de Strasbourg, CNRS, Architecture et Réactivité de l'ARN, UPR9002, F-67000 Strasbourg, France
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8
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Bartova S, Pechlaner M, Donghi D, Sigel RKO. Studying metal ion binding properties of a three-way junction RNA by heteronuclear NMR. J Biol Inorg Chem 2016; 21:319-28. [PMID: 26880094 DOI: 10.1007/s00775-016-1341-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2015] [Accepted: 01/25/2016] [Indexed: 10/22/2022]
Abstract
Self-splicing group II introns are highly structured RNA molecules, containing a characteristic secondary and catalytically active tertiary structure, which is formed only in the presence of Mg(II). Mg(II) initiates the first folding step governed by the κζ element within domain 1 (D1κζ). We recently solved the NMR structure of D1κζ derived from the mitochondrial group II intron ribozyme Sc.ai5γ and demonstrated that Mg(II) is essential for its stabilization. Here, we performed a detailed multinuclear NMR study of metal ion interactions with D1κζ, using Cd(II) and cobalt(III)hexammine to probe inner- and outer-sphere coordination of Mg(II) and thus to better characterize its binding sites. Accordingly, we mapped (1)H, (15)N, (13)C, and (31)P spectral changes upon addition of different amounts of the metal ions. Our NMR data reveal a Cd(II)-assisted macrochelate formation at the 5'-end triphosphate, a preferential Cd(II) binding to guanines in a helical context, an electrostatic interaction in the ζ tetraloop receptor and various metal ion interactions in the GAAA tetraloop and κ element. These results together with our recently published data on Mg(II) interaction provide a much better understanding of Mg(II) binding to D1κζ, and reveal how intricate and complex metal ion interactions can be.
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Affiliation(s)
- Simona Bartova
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.,Department of Analytical Chemistry, University of Chemistry and Technology Prague, Technická 5, 166 28, Prague, Czech Republic
| | - Maria Pechlaner
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.,Institute for Molecular Modeling and Simulation, University of Natural Resources and Life Sciences (BOKU), Muthgasse 18, 1190, Vienna, Austria
| | - Daniela Donghi
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
| | - Roland K O Sigel
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
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9
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Karplus PA, Diederichs K. Assessing and maximizing data quality in macromolecular crystallography. Curr Opin Struct Biol 2015. [PMID: 26209821 DOI: 10.1016/j.sbi.2015.07.003] [Citation(s) in RCA: 166] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The quality of macromolecular crystal structures depends, in part, on the quality and quantity of the data used to produce them. Here, we review recent shifts in our understanding of how to use data quality indicators to select a high resolution cutoff that leads to the best model, and of the potential to greatly increase data quality through the merging of multiple measurements from multiple passes of single crystals or from multiple crystals. Key factors supporting this shift are the introduction of more robust correlation coefficient based indicators of the precision of merged data sets as well as the recognition of the substantial useful information present in extensive amounts of data once considered too weak to be of value.
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Affiliation(s)
- P Andrew Karplus
- Department of Biochemistry & Biophysics, Oregon State University, Corvallis, OR 97331, USA.
| | - Kay Diederichs
- University of Konstanz, Faculty of Biology, Box 647, D-78457 Konstanz, Germany.
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10
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Skilandat M, Sigel RKO. The role of Mg(II) in DNA cleavage site recognition in group II intron ribozymes: solution structure and metal ion binding sites of the RNA-DNA complex. J Biol Chem 2015; 289:20650-63. [PMID: 24895129 DOI: 10.1074/jbc.m113.542381] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Group II intron ribozymes catalyze the cleavage of (and their reinsertion into) DNA and RNA targets using a Mg2(+)-dependent reaction. The target is cleaved 3' to the last nucleotide of intron binding site 1 (IBS1), one of three regions that form base pairs with the intron's exon binding sites (EBS1 to -3).We solved the NMR solution structure of the d3' hairpin of the Sc.ai5γ intron containing EBS1 in its 11-nucleotide loop in complex with the dIBS1 DNA 7-mer and compare it with the analogous RNA-RNA contact. The EBS1-dIBS1 helix is slightly flexible and non-symmetric. NMR data reveal two major groove binding sites for divalent metal ions at the EBS1-dIBS1 helix, and surface plasmon resonance experiments show that low concentrations of Mg2(+) considerably enhance the affinity of dIBS1 for EBS1. Our results indicate that identification of both RNA and DNA IBS1 targets, presentation of the scissile bond, and stabilization of the structure by metal ions are governed by the overall structure of EBS1-dIBS1 and the surrounding loop nucleotides but are irrespective of different EBS1-(d)IBS1 geometries and interstrand affinities.
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11
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Wang J, Li Y, Modis Y. Exploiting subtle structural differences in heavy-atom derivatives for experimental phasing. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2014; 70:1873-83. [PMID: 25004964 PMCID: PMC4089484 DOI: 10.1107/s1399004714008943] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2014] [Accepted: 04/19/2014] [Indexed: 02/02/2023]
Abstract
Structure determination using the single isomorphous replacement (SIR) or single-wavelength anomalous diffraction (SAD) methods with weak derivatives remains very challenging. In a recent structure determination of glycoprotein E2 from bovine viral diarrhea virus, three isomorphous uranium-derivative data sets were merged to obtain partially interpretable initial experimental maps. Small differences between them were then exploited by treating them as three independent SAD data sets plus three circular pairwise SIR data sets to improve the experimental maps. Here, how such subtle structural differences were exploited for experimental phasing is described in detail. The basis for why this approach works is also provided: the effective resolution of isomorphous signals between highly isomorphous derivatives is often much higher than the effective resolution of the anomalous signals of individual derivative data sets. Hence, the new phasing approaches outlined here will be generally applicable to structure determinations involving weak derivatives.
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Affiliation(s)
- Jimin Wang
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Yue Li
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Yorgo Modis
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
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12
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Wang J, Wing RA. Diamonds in the rough: a strong case for the inclusion of weak-intensity X-ray diffraction data. ACTA ACUST UNITED AC 2014; 70:1491-7. [PMID: 24816117 DOI: 10.1107/s1399004714005318] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2013] [Accepted: 03/07/2014] [Indexed: 11/11/2022]
Abstract
Overwhelming evidence exists to show that the inclusion of weak-intensity, high-resolution X-ray diffraction data helps improve the refinement of atomic models by imposing strong constraints on individual and overall temperature B factors and thus the quality of crystal structures. Some researchers consider these data to be of little value and opt to discard them during data processing, particularly at medium and low resolution, at which individual B factors of atomic models cannot be refined. Here, new evidence is provided to show that the inclusion of these data helps to improve the quality of experimental phases by imposing proper constraints on electron-density models during noncrystallographic symmetry (NCS) averaging. Using electron-density correlation coefficients as criteria, the resolution of data has successfully been extended from 3.1 to 2.5 Å resolution with redundancy-independent merging R factors from below 100% to about 310%. It is further demonstrated that phase information can be fully extracted from observed amplitudes through de novo NCS averaging. Averaging starts with uniform density inside double-shelled spherical masks and NCS matrices that are derived from bound heavy-atom clusters at the vertices of cuboctahedrally symmetric protein particles.
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Affiliation(s)
- Jimin Wang
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Richard A Wing
- Laboratory of Cell Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA
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13
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Ritacco CJ, Steitz TA, Wang J. Exploiting large non-isomorphous differences for phase determination of a G-segment invertase-DNA complex. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2014; 70:685-93. [PMID: 24598738 PMCID: PMC3949525 DOI: 10.1107/s1399004713032392] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Accepted: 11/27/2013] [Indexed: 11/10/2022]
Abstract
Crystals of the G-segment invertase in complex with a 37-base-pair asymmetric DNA duplex substrate had an unusually high solvent content of 88% and diffracted to a maximal resolution of about 5.0 Å. These crystals exhibited a high degree of non-isomorphism and anisotropy, which presented a serious challenge for structure determination by isomorphous replacement. Here, a procedure of cross-crystal averaging is described that uses large non-isomorphous crystallographic data with a priori information of an approximate molecular boundary as determined from a minimal amount of experimental phase information. Using this procedure, high-quality experimental phases were obtained that have enabled it to be shown that the conformation of the bound substrate DNA duplex significantly differs from those of substrates bound in other serine recombinase-DNA complexes.
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Affiliation(s)
- Christopher J. Ritacco
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Thomas A. Steitz
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
- Department of Chemistry, Yale University, New Haven, CT 06520, USA
- Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA
| | - Jimin Wang
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
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14
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Anokhina M, Bessonov S, Miao Z, Westhof E, Hartmuth K, Lührmann R. RNA structure analysis of human spliceosomes reveals a compact 3D arrangement of snRNAs at the catalytic core. EMBO J 2013; 32:2804-18. [PMID: 24002212 DOI: 10.1038/emboj.2013.198] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2012] [Accepted: 07/24/2013] [Indexed: 11/09/2022] Open
Abstract
Although U snRNAs play essential roles in splicing, little is known about the 3D arrangement of U2, U6, and U5 snRNAs and the pre-mRNA in active spliceosomes. To elucidate their relative spatial organization and dynamic rearrangement, we examined the RNA structure of affinity-purified, human spliceosomes before and after catalytic step 1 by chemical RNA structure probing. We found a stable 3-way junction of the U2/U6 snRNA duplex in active spliceosomes that persists minimally through step 1. Moreover, the formation of alternating, mutually exclusive, U2 snRNA conformations, as observed in yeast, was not detected in different assembly stages of human spliceosomal complexes (that is, B, B(act), or C complexes). Psoralen crosslinking revealed an interaction during/after step 1 between internal loop 1 of the U5 snRNA, and intron nucleotides immediately downstream of the branchpoint. Using the experimentally derived structural constraints, we generated a model of the RNA network of the step 1 spliceosome, based on the crystal structure of a group II intron through homology modelling. The model is topologically consistent with current genetic, biochemical, and structural data.
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Affiliation(s)
- Maria Anokhina
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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15
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Gangnard S, Badaut C, Ramboarina S, Baron B, Ramdani T, Gamain B, Deloron P, Lewit-Bentley A, Bentley GA. Structural and immunological correlations between the variable blocks of the VAR2CSA domain DBL6ε from two Plasmodium falciparum parasite lines. J Mol Biol 2013; 425:1697-711. [PMID: 23429057 DOI: 10.1016/j.jmb.2013.02.014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Revised: 01/23/2013] [Accepted: 02/11/2013] [Indexed: 11/29/2022]
Abstract
Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1), a family of adhesins of the falciparum species of the malaria parasite, is exposed on the surface of the infected erythrocyte. In general, only one PfEMP1 variant is expressed at a time but switching between variants occurs, changing both host-cell receptor specificity and serotype. The PfEMP1 variant VAR2CSA causes sequestration of infected erythrocytes in the intervillous spaces of the placenta via the glycosaminoglycan chondroitin sulfate A. This leads to pregnancy-associated malaria, which has severe consequences for the fetus and mother. The extracellular region of VAR2CSA comprises six DBL (Duffy-binding-like) domains and a single CIDR (cysteine-rich inter-domain region) domain. The C-terminal domain DBL6ε, the most polymorphic domain of VAR2CSA, has seven regions of high variability termed variable blocks (VBs). Here we have determined the crystal structure of DBL6ε from the FCR3 parasite line and have compared it with the previously determined structure of that from the 3D7 line. We found significant differences particularly in the N-terminal region, which contains the first VB (VB1). Although DBL6ε is the most variable VAR2CSA domain, DBL6ε-FCR3 and DBL6ε-3D7 react with IgG purified from immune sera of pregnant women. Furthermore, IgG purified on one domain cross-reacts with the other, confirming the presence of cross-reactive epitopes. We also examined reactivity of immune sera to the four least variable VB (VB1, VB2, VB4 and VB5) using peptides with the consensus sequence closest, in turn, to the FCR3 or 3D7 domain. These results provide new molecular insights into immune escape by parasites expressing the VAR2CSA variant.
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Affiliation(s)
- Stéphane Gangnard
- Unité d'Immunologie Structurale, Département de Biologie Structurale et Chimie, Institut Pasteur, 25 rue du Docteur Roux, 75724 Paris, France
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16
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Ritacco CJ, Kamtekar S, Wang J, Steitz TA. Crystal structure of an intermediate of rotating dimers within the synaptic tetramer of the G-segment invertase. Nucleic Acids Res 2013; 41:2673-82. [PMID: 23275567 PMCID: PMC3575834 DOI: 10.1093/nar/gks1303] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The serine family of site-specific DNA recombination enzymes accomplishes strand cleavage, exchange and religation using a synaptic protein tetramer. A double-strand break intermediate in which each protein subunit is covalently linked to the target DNA substrate ensures that the recombination event will not damage the DNA. The previous structure of a tetrameric synaptic complex of γδ resolvase linked to two cleaved DNA strands had suggested a rotational mechanism of recombination in which one dimer rotates 180° about the flat exchange interface for strand exchange. Here, we report the crystal structure of a synaptic tetramer of an unliganded activated mutant (M114V) of the G-segment invertase (Gin) in which one dimer half is rotated by 26° or 154° relative to the other dimer when compared with the dimers in the synaptic complex of γδ resolvase. Modeling shows that this rotational orientation of Gin is not compatible with its being able to bind uncleaved DNA, implying that this structure represents an intermediate in the process of strand exchange. Thus, our structure provides direct evidence for the proposed rotational mechanism of site-specific recombination.
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Affiliation(s)
- Christopher J. Ritacco
- Department of Molecular Biophysics and Biochemistry, Department of Chemistry and Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA
| | - Satwik Kamtekar
- Department of Molecular Biophysics and Biochemistry, Department of Chemistry and Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA
| | - Jimin Wang
- Department of Molecular Biophysics and Biochemistry, Department of Chemistry and Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA
| | - Thomas A. Steitz
- Department of Molecular Biophysics and Biochemistry, Department of Chemistry and Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA
- *To whom correspondence should be addressed. Tel: +203 432 5617; Fax: +203 432 3282;
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17
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Donghi D, Pechlaner M, Finazzo C, Knobloch B, Sigel RKO. The structural stabilization of the κ three-way junction by Mg(II) represents the first step in the folding of a group II intron. Nucleic Acids Res 2012; 41:2489-504. [PMID: 23275550 PMCID: PMC3575829 DOI: 10.1093/nar/gks1179] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Folding of group II introns is characterized by a first slow compaction of domain 1 (D1) followed by the rapid docking of other domains to this scaffold. D1 compaction initiates in a small subregion encompassing the κ and ζ elements. These two tertiary elements are also the major interaction sites with domain 5 to form the catalytic core. Here, we provide the first characterization of the structure adopted at an early folding step and show that the folding control element can be narrowed down to the three-way junction with the κ motif. In our nuclear magnetic resonance studies of this substructure derived from the yeast mitochondrial group II intron Sc.ai5γ, we show that a high affinity Mg(II) ion stabilizes the κ element and enables coaxial stacking between helices d′ and d′′, favoring a rigid duplex across the three-way junction. The κ-element folds into a stable GAAA-tetraloop motif and engages in A-minor interactions with helix d′. The addition of cobalt(III)hexammine reveals three distinct binding sites. The Mg(II)-promoted structural rearrangement and rigidification of the D1 core can be identified as the first micro-step of D1 folding.
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Affiliation(s)
- Daniela Donghi
- Institute of Inorganic Chemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
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18
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Structural and mechanistic insights into guanylylation of RNA-splicing ligase RtcB joining RNA between 3'-terminal phosphate and 5'-OH. Proc Natl Acad Sci U S A 2012; 109:15235-40. [PMID: 22949672 DOI: 10.1073/pnas.1213795109] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The RtcB protein has recently been identified as a 3'-phosphate RNA ligase that directly joins an RNA strand ending with a 2',3'-cyclic phosphate to the 5'-hydroxyl group of another RNA strand in a GTP/Mn(2+)-dependent reaction. Here, we report two crystal structures of Pyrococcus horikoshii RNA-splicing ligase RtcB in complex with Mn(2+) alone (RtcB/ Mn(2+)) and together with a covalently bound GMP (RtcB-GMP/Mn(2+)). The RtcB/ Mn(2+) structure (at 1.6 Å resolution) shows two Mn(2+) ions at the active site, and an array of sulfate ions nearby that indicate the binding sites of the RNA phosphate backbone. The structure of the RtcB-GMP/Mn(2+) complex (at 2.3 Å resolution) reveals the detailed geometry of guanylylation of histidine 404. The critical roles of the key residues involved in the binding of the two Mn(2+) ions, the four sulfates, and GMP are validated in extensive mutagenesis and biochemical experiments, which also provide a thorough characterization for the three steps of the RtcB ligation pathway: (i) guanylylation of the enzyme, (ii) guanylyl-transfer to the RNA substrate, and (iii) overall ligation. These results demonstrate that the enzyme's substrate-induced GTP binding site and the putative reactive RNA ends are in the vicinity of the binuclear Mn(2+) active center, which provides detailed insight into how the enzyme-bound GMP is tansferred to the 3'-phosphate of the RNA substrate for activation and subsequent nucleophilic attack by the 5'-hydroxyl of the second RNA substrate, resulting in the ligated product and release of GMP.
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19
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Hori N, Takada S. Coarse-Grained Structure-Based Model for RNA-Protein Complexes Developed by Fluctuation Matching. J Chem Theory Comput 2012; 8:3384-94. [DOI: 10.1021/ct300361j] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Naoto Hori
- Department of Biophysics,
Graduate
School of Science, Kyoto University, Kyoto, Japan
| | - Shoji Takada
- Department of Biophysics,
Graduate
School of Science, Kyoto University, Kyoto, Japan
- Core Research for Evolutional
Science and Technology, Japan Science and Technology Agency, Japan
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20
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Abstract
In macromolecular x-ray crystallography, refinement R values measure the agreement between observed and calculated data. Analogously, R(merge) values reporting on the agreement between multiple measurements of a given reflection are used to assess data quality. Here, we show that despite their widespread use, R(merge) values are poorly suited for determining the high-resolution limit and that current standard protocols discard much useful data. We introduce a statistic that estimates the correlation of an observed data set with the underlying (not measurable) true signal; this quantity, CC*, provides a single statistically valid guide for deciding which data are useful. CC* also can be used to assess model and data quality on the same scale, and this reveals when data quality is limiting model improvement.
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Affiliation(s)
- P Andrew Karplus
- Department of Biochemistry and Biophysics, Oregon State University, Corvallis, OR 97331, USA
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21
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Hamdani HY, Appasamy SD, Willett P, Artymiuk PJ, Firdaus-Raih M. NASSAM: a server to search for and annotate tertiary interactions and motifs in three-dimensional structures of complex RNA molecules. Nucleic Acids Res 2012; 40:W35-41. [PMID: 22661578 PMCID: PMC3394293 DOI: 10.1093/nar/gks513] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Similarities in the 3D patterns of RNA base interactions or arrangements can provide insights into their functions and roles in stabilization of the RNA 3D structure. Nucleic Acids Search for Substructures and Motifs (NASSAM) is a graph theoretical program that can search for 3D patterns of base arrangements by representing the bases as pseudo-atoms. The geometric relationship of the pseudo-atoms to each other as a pattern can be represented as a labeled graph where the pseudo-atoms are the graph’s nodes while the edges are the inter-pseudo-atomic distances. The input files for NASSAM are PDB formatted 3D coordinates. This web server can be used to identify matches of base arrangement patterns in a query structure to annotated patterns that have been reported in the literature or that have possible functional and structural stabilization implications. The NASSAM program is freely accessible without any login requirement at http://mfrlab.org/grafss/nassam/.
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Affiliation(s)
- Hazrina Y Hamdani
- School of Biosciences and Biotechnology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Malaysia
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22
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Vitali J, Singh AK, Soares AS, Colaneri MJ. Structure of the catalytic chain of Methanococcus jannaschii aspartate transcarbamoylase in a hexagonal crystal form: insights into the path of carbamoyl phosphate to the active site of the enzyme. Acta Crystallogr Sect F Struct Biol Cryst Commun 2012; 68:527-34. [PMID: 22691781 PMCID: PMC3374506 DOI: 10.1107/s1744309112011037] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2011] [Accepted: 03/13/2012] [Indexed: 11/10/2022]
Abstract
Crystals of the catalytic chain of Methanococcus jannaschii aspartate transcarbamoylase (ATCase) grew in the presence of the regulatory chain in the hexagonal space group P6(3)22, with one monomer per asymmetric unit. This is the first time that crystals with only one monomer in the asymmetric unit have been obtained; all known structures of the catalytic subunit contain several crystallographically independent monomers. The symmetry-related chains form the staggered dimer of trimers observed in the other known structures of the catalytic subunit. The central channel of the catalytic subunit contains a sulfate ion and a K(+) ion as well as a glycerol molecule at its entrance. It is possible that it is involved in channeling carbamoyl phosphate (CP) to the active site of the enzyme. A second sulfate ion near Arg164 is near the second CP position in the wild-type Escherichia coli ATCase structure complexed with CP. It is suggested that this position may also be in the path that CP takes when binding to the active site in a partial diffusion process at 310 K. Additional biochemical studies of carbamoylation and the molecular organization of this enzyme in M. jannaschii will provide further insight into these points.
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Affiliation(s)
- Jacqueline Vitali
- Department of Physics, Cleveland State University, Euclid Avenue at East 24th Street, Cleveland, OH 44115, USA.
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23
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Chan RT, Robart AR, Rajashankar KR, Pyle AM, Toor N. Crystal structure of a group II intron in the pre-catalytic state. Nat Struct Mol Biol 2012; 19:555-7. [PMID: 22484319 DOI: 10.1038/nsmb.2270] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Accepted: 02/27/2012] [Indexed: 11/09/2022]
Abstract
Group II introns are self-splicing catalytic RNAs that are thought to be ancestral to the spliceosome. Here we report the 3.65-Å crystal structure of the group II intron from Oceanobacillus iheyensis in the pre-catalytic state. The structure reveals the conformation of the 5' splice site in the catalytic core and represents the first structure of an intron prior to the first step of splicing.
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Affiliation(s)
- Russell T Chan
- Department of Chemistry and Biochemistry, University of California, San Diego, San Diego, California, USA
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24
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Xia S, Eom SH, Konigsberg WH, Wang J. Structural basis for differential insertion kinetics of dNMPs opposite a difluorotoluene nucleotide residue. Biochemistry 2012; 51:1476-85. [PMID: 22304682 DOI: 10.1021/bi2016487] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
We have recently challenged the widely held view that 2,4-difluorotoluene (dF) is a nonpolar isosteric analogue of the nucleotide dT, incapable of forming hydrogen bonds (HBs). To gain a further understanding for the kinetic preference that favors dAMP insertion opposite a templating dF, a result that mirrors the base selectivity that favors dAMP insertion opposite dT by RB69 DNA polymerase (RB69pol), we determined presteady-state kinetic parameters for incorporation of four dNMPs opposite dF by RB69pol and solved the structures of corresponding ternary complexes. We observed that both the F2 and F4 substituent of dF in these structures serve as HB acceptors forming HBs either directly with dTTP and dGTP or indirectly with dATP and dCTP via ordered water molecules. We have defined the shape and chemical features of each dF/dNTP pair in the RB69pol active site without the corresponding phosphodiester-linkage constraints of dF/dNs when they are embedded in isolated DNA duplexes. These features can explain the kinetic preferences exhibited by the templating dF when the nucleotide incorporation is catalyzed by wild type RB69pol or its mutants. We further show that the shapes of the dNTP/dF nascent base pair differ markedly from the corresponding dNTP/dT in the pol active site and that these differences have a profound effect on their incorporation efficiencies.
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Affiliation(s)
- Shuangluo Xia
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8114, United States
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25
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Linking the branchpoint helix to a newly found receptor allows lariat formation by a group II intron. EMBO J 2011; 30:3040-51. [PMID: 21712813 DOI: 10.1038/emboj.2011.214] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Accepted: 06/03/2011] [Indexed: 11/08/2022] Open
Abstract
Like spliceosomal introns, the ribozyme-containing group II introns are excised as branched, lariat structures: a 2'-5' bond is created between the first nucleotide of the intron and an adenosine in domain VI, a component which is missing from available crystal structures of the ribozyme. Comparative sequence analysis, modelling and nucleotide substitutions point to the existence, and probable location, of a specific RNA receptor for the section of domain VI that lies just distal to the branchpoint adenosine. By designing oligonucleotides that tether domain VI to this novel binding site, we have been able to specifically activate lariat formation in an engineered, defective group II ribozyme. The location of the newly identified receptor implies that prior to exon ligation, the distal part of domain VI undergoes a major translocation, which can now be brought under control by the system of anchoring oligonucleotides we have developed. Interestingly, these oligonucleotides, which link the branchpoint helix and the binding site for intron nucleotides 3-4, may be viewed as counterparts of U2-U6 helix III in the spliceosome.
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