1
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Smith CR, Kulyk S, Ahmad MUD, Arkhipova V, Christensen JG, Gunn RJ, Ivetac A, Ketcham JM, Kuehler J, Lawson JD, Thomas NC, Wang X, Marx MA. Fragment optimization and elaboration strategies - the discovery of two lead series of PRMT5/MTA inhibitors from five fragment hits. RSC Med Chem 2022; 13:1549-1564. [PMID: 36545438 PMCID: PMC9749961 DOI: 10.1039/d2md00163b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Accepted: 08/27/2022] [Indexed: 12/24/2022] Open
Abstract
Here we describe the early stages of a fragment-based lead discovery (FBLD) project for a recently elucidated synthetic lethal target, the PRMT5/MTA complex, for the treatment of MTAP-deleted cancers. Starting with five fragment/PRMT5/MTA X-ray co-crystal structures, we employed a two-phase fragment elaboration process encompassing optimization of fragment hits and subsequent fragment growth to increase potency, assess synthetic tractability, and enable structure-based drug design. Two lead series were identified, one of which led to the discovery of the clinical candidate MRTX1719.
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Affiliation(s)
| | | | | | | | | | | | | | | | - Jon Kuehler
- Mirati TherapeuticsSan DiegoCalifornia92121USA
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2
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d'Amico EA, Ud Din Ahmad M, Cmentowski V, Girbig M, Müller F, Wohlgemuth S, Brockmeyer A, Maffini S, Janning P, Vetter IR, Carter AP, Perrakis A, Musacchio A. Conformational transitions of the Spindly adaptor underlie its interaction with Dynein and Dynactin. J Cell Biol 2022; 221:213466. [PMID: 36107127 PMCID: PMC9481740 DOI: 10.1083/jcb.202206131] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 08/02/2022] [Accepted: 08/17/2022] [Indexed: 11/22/2022] Open
Abstract
Cytoplasmic Dynein 1, or Dynein, is a microtubule minus end-directed motor. Dynein motility requires Dynactin and a family of activating adaptors that stabilize the Dynein-Dynactin complex and promote regulated interactions with cargo in space and time. How activating adaptors limit Dynein activation to specialized subcellular locales is unclear. Here, we reveal that Spindly, a mitotic Dynein adaptor at the kinetochore corona, exists natively in a closed conformation that occludes binding of Dynein-Dynactin to its CC1 box and Spindly motif. A structure-based analysis identified various mutations promoting an open conformation of Spindly that binds Dynein-Dynactin. A region of Spindly downstream from the Spindly motif and not required for cargo binding faces the CC1 box and stabilizes the intramolecular closed conformation. This region is also required for robust kinetochore localization of Spindly, suggesting that kinetochores promote Spindly activation to recruit Dynein. Thus, our work illustrates how specific Dynein activation at a defined cellular locale may require multiple factors.
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Affiliation(s)
- Ennio A d'Amico
- Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Misbha Ud Din Ahmad
- Oncode Institute and Department of Biochemistry, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Verena Cmentowski
- Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany.,Centre for Medical Biotechnology, Faculty of Biology, University Duisburg-Essen, Essen, Germany
| | | | - Franziska Müller
- Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Sabine Wohlgemuth
- Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Andreas Brockmeyer
- Department of Chemical Biology, Max-Planck-Institute of Molecular Physiology, Dortmund, Germany
| | - Stefano Maffini
- Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Petra Janning
- Department of Chemical Biology, Max-Planck-Institute of Molecular Physiology, Dortmund, Germany
| | - Ingrid R Vetter
- Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | | | - Anastassis Perrakis
- Oncode Institute and Department of Biochemistry, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Andrea Musacchio
- Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany.,Centre for Medical Biotechnology, Faculty of Biology, University Duisburg-Essen, Essen, Germany
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3
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Elings W, Chikunova A, van Zanten DB, Drenth R, Ahmad MUD, Blok AJ, Timmer M, Perrakis A, Ubbink M. Two β-Lactamase Variants with Reduced Clavulanic Acid Inhibition Display Different Millisecond Dynamics. Antimicrob Agents Chemother 2021; 65:e0262820. [PMID: 34031049 PMCID: PMC8284444 DOI: 10.1128/aac.02628-20] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2020] [Accepted: 05/07/2021] [Indexed: 11/20/2022] Open
Abstract
The β-lactamase of Mycobacterium tuberculosis, BlaC, is susceptible to inhibition by clavulanic acid. The ability of this enzyme to escape inhibition through mutation was probed using error-prone PCR combined with functional screening in Escherichia coli. The variant that was found to confer the most inhibitor resistance, K234R, as well as variant G132N that was found previously were characterized using X-ray crystallography and nuclear magnetic resonance (NMR) relaxation experiments to probe structural and dynamic properties. The G132N mutant exists in solution in two almost equally populated conformations that exchange with a rate of ca. 88 s-1. The conformational change affects a broad region of the enzyme. The crystal structure reveals that the Asn132 side chain forces the peptide bond between Ser104 and Ile105 in a cis-conformation. The crystal structure suggests multiple conformations for several side chains (e.g., Ser104 and Ser130) and a short loop (positions 214 to 216). In the K234R mutant, the active-site dynamics are significantly diminished with respect to the wild-type enzyme. These results show that multiple evolutionary routes are available to increase inhibitor resistance in BlaC and that active-site dynamics on the millisecond time scale are not required for catalytic function.
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Affiliation(s)
- Wouter Elings
- Leiden Institute of Chemistry, Leiden University, Leiden, The Netherlands
| | | | | | - Ralphe Drenth
- Leiden Institute of Chemistry, Leiden University, Leiden, The Netherlands
| | - Misbha Ud Din Ahmad
- Division of Biochemistry, the Netherlands Cancer Institute, Amsterdam, The Netherlands
- Oncode Institute, Amsterdam, The Netherlands
| | - Anneloes J. Blok
- Leiden Institute of Chemistry, Leiden University, Leiden, The Netherlands
| | - Monika Timmer
- Leiden Institute of Chemistry, Leiden University, Leiden, The Netherlands
| | - Anastassis Perrakis
- Division of Biochemistry, the Netherlands Cancer Institute, Amsterdam, The Netherlands
- Oncode Institute, Amsterdam, The Netherlands
| | - Marcellus Ubbink
- Leiden Institute of Chemistry, Leiden University, Leiden, The Netherlands
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4
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van Alen I, Chikunova A, Safeer AA, Ahmad MUD, Perrakis A, Ubbink M. The G132S Mutation Enhances the Resistance of Mycobacterium tuberculosis β-Lactamase against Sulbactam. Biochemistry 2021; 60:2236-2245. [PMID: 34250791 PMCID: PMC8383266 DOI: 10.1021/acs.biochem.1c00168] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
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The current rise
of antibiotic resistant forms of Mycobacterium
tuberculosis is a global health threat that calls for new
antibiotics. The β-lactamase BlaC of this pathogen prevents
the use of β-lactam antibiotics, except in combination with
a β-lactamase inhibitor. To understand if exposure to such inhibitors
can easily result in resistance, a BlaC evolution experiment was performed,
studying the evolutionary adaptability against the inhibitor sulbactam.
Several amino acid substitutions in BlaC were shown to confer reduced
sensitivity to sulbactam. The G132S mutation causes a reduction in
the rate of nitrocefin and ampicillin hydrolysis and simultaneously
reduces the sensitivity for sulbactam inhibition. Introduction of
the side chain moiety of Ser132 causes the 104–105 peptide
bond to assume the cis conformation and the side
chain of Ser104 to be rotated toward the sulbactam adduct with which
it forms a hydrogen bond not present in the wild-type enzyme. The
gatekeeper residue Ile105 also moves. These changes in the entrance
of the active site can explain the decreased affinity of G132S BlaC
for both substrates and sulbactam. Our results show that BlaC can
easily acquire a reduced sensitivity for sulbactam, with a single-amino
acid mutation, which could hinder the use of combination therapies.
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Affiliation(s)
- Ilona van Alen
- Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333CC Leiden, The Netherlands
| | - Aleksandra Chikunova
- Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333CC Leiden, The Netherlands
| | - Adil A Safeer
- Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333CC Leiden, The Netherlands
| | - Misbha Ud Din Ahmad
- Division of Biochemistry, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
| | - Anastassis Perrakis
- Division of Biochemistry, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
| | - Marcellus Ubbink
- Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333CC Leiden, The Netherlands
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5
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Ahmad MUD, Fish A, Molenaar J, Sreeramulu S, Richter C, Altincekic N, Schwalbe H, Wienk H, Perrakis A. Nano-Differential Scanning Fluorimetry for Screening in Fragment-based Lead Discovery. J Vis Exp 2021. [PMID: 34057451 DOI: 10.3791/62469] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Thermal shift assays (TSAs) examine how the melting temperature (Tm) of a target protein changes in response to changes in its environment (e.g., buffer composition). The utility of TSA, and specifically of nano-Differential Scanning Fluorimetry (nano-DSF), has been established over the years, both for finding conditions that help stabilize a specific protein and for looking at ligand binding by monitoring changes in the apparent Tm. This paper presents an efficient screening of the Diamond-SGC-iNEXT Poised (DSi-Poised) fragment library (768 compounds) by the use of nano-DSF, monitoring Tm to identify potential fragment binding. The prerequisites regarding protein quality and concentration for performing nano-DSF experiments are briefly outlined followed by a step-by-step protocol that uses a nano-liter robotic dispenser commonly used in structural biology laboratories for preparing the required samples in 96-well plates. The protocol describes how the reagent mixtures are transferred to the capillaries needed for nano-DSF measurements. In addition, this paper provides protocols to measure thermal denaturation (monitoring intrinsic tryptophan fluorescence) and aggregation (monitoring light back-scattering) and the subsequent steps for data transfer and analysis. Finally, screening experiments with three different protein targets are discussed to illustrate the use of this procedure in the context of lead discovery campaigns. The overall principle of the method described can be easily transferred to other fragment libraries or adapted to other instruments.
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Affiliation(s)
- Misbha Ud Din Ahmad
- Oncode Institute and Division of Biochemistry, the Netherlands Cancer Institute
| | - Alexander Fish
- Oncode Institute and Division of Biochemistry, the Netherlands Cancer Institute
| | - Jeroen Molenaar
- Oncode Institute and Division of Biochemistry, the Netherlands Cancer Institute
| | - Sridhar Sreeramulu
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-University
| | - Christian Richter
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-University
| | - Nadide Altincekic
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-University
| | - Harald Schwalbe
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-University
| | - Hans Wienk
- Oncode Institute and Division of Biochemistry, the Netherlands Cancer Institute
| | - Anastassis Perrakis
- Oncode Institute and Division of Biochemistry, the Netherlands Cancer Institute;
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6
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Chikunova A, Manley MP, Ud Din Ahmad M, Bilman T, Perrakis A, Ubbink M. Conserved residues Glu37 and Trp229 play an essential role in protein folding of β‐lactamase. FEBS J 2021; 288:5708-5722. [PMID: 33792206 PMCID: PMC8518976 DOI: 10.1111/febs.15854] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Revised: 02/26/2021] [Accepted: 03/30/2021] [Indexed: 01/27/2023]
Abstract
Evolutionary robustness requires that the number of highly conserved amino acid residues in proteins is minimized. In enzymes, such conservation is observed for catalytic residues but also for some residues in the second shell or even further from the active site. β‐Lactamases evolve in response to changing antibiotic selection pressures and are thus expected to be evolutionarily robust, with a limited number of highly conserved amino acid residues. As part of the effort to understand the roles of conserved residues in class A β‐lactamases, we investigate the reasons leading to the conservation of two amino acid residues in the β‐lactamase BlaC, Glu37, and Trp229. Using site‐directed mutagenesis, we have generated point mutations of these residues and observed a drastic decrease in the levels of soluble protein produced in Escherichia coli, thus abolishing completely the resistance of bacteria against β‐lactam antibiotics. However, the purified proteins are structurally and kinetically very similar to the wild‐type enzyme, only differing by exhibiting a slightly lower melting temperature. We conclude that conservation of Glu37 and Trp229 is solely caused by an essential role in the folding process, and we propose that during folding Glu37 primes the formation of the central β‐sheet and Trp229 contributes to the hydrophobic collapse into a molten globule.
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Affiliation(s)
| | - Max P. Manley
- Leiden Institute of Chemistry Leiden University the Netherlands
| | - Misbha Ud Din Ahmad
- Oncode Institute and Division of Biochemistry the Netherlands Cancer Institute Amsterdam the Netherlands
| | - Tuğçe Bilman
- Leiden Institute of Chemistry Leiden University the Netherlands
| | - Anastassis Perrakis
- Oncode Institute and Division of Biochemistry the Netherlands Cancer Institute Amsterdam the Netherlands
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7
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Sacristan C, Ahmad MUD, Keller J, Fermie J, Groenewold V, Tromer E, Fish A, Melero R, Carazo JM, Klumperman J, Musacchio A, Perrakis A, Kops GJ. Dynamic kinetochore size regulation promotes microtubule capture and chromosome biorientation in mitosis. Nat Cell Biol 2018; 20:800-810. [PMID: 29915359 PMCID: PMC6485389 DOI: 10.1038/s41556-018-0130-3] [Citation(s) in RCA: 68] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Accepted: 05/22/2018] [Indexed: 01/28/2023]
Abstract
Faithful chromosome segregation depends on the ability of sister kinetochores to attach to spindle microtubules. The outer layer of kinetochores transiently expands in early mitosis to form a fibrous corona, and compacts following microtubule capture. Here we show that the dynein adaptor Spindly and the RZZ (ROD-Zwilch-ZW10) complex drive kinetochore expansion in a dynein-independent manner. C-terminal farnesylation and MPS1 kinase activity cause conformational changes of Spindly that promote oligomerization of RZZ-Spindly complexes into a filamentous meshwork in cells and in vitro. Concurrent with kinetochore expansion, Spindly potentiates kinetochore compaction by recruiting dynein via three conserved short linear motifs. Expanded kinetochores unable to compact engage in extensive, long-lived lateral microtubule interactions that persist to metaphase, and result in merotelic attachments and chromosome segregation errors in anaphase. Thus, dynamic kinetochore size regulation in mitosis is coordinated by a single, Spindly-based mechanism that promotes initial microtubule capture and subsequent correct maturation of attachments.
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Affiliation(s)
- Carlos Sacristan
- Oncode Institute, Hubrecht Institute-KNAW and University Medical Center Utrecht, Utrecht, The Netherlands
| | - Misbha Ud Din Ahmad
- Department of Biochemistry, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Jenny Keller
- Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Job Fermie
- Section Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands
| | - Vincent Groenewold
- Section Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands
| | - Eelco Tromer
- Oncode Institute, Hubrecht Institute-KNAW and University Medical Center Utrecht, Utrecht, The Netherlands
| | - Alexander Fish
- Department of Biochemistry, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Roberto Melero
- Biocomputing Unit, National Center for Biotechnology (CSIC), Darwin 3, Campus Universidad Autónoma, Madrid, Spain
| | - José María Carazo
- Biocomputing Unit, National Center for Biotechnology (CSIC), Darwin 3, Campus Universidad Autónoma, Madrid, Spain
| | - Judith Klumperman
- Section Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands
| | - Andrea Musacchio
- Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany.,Centre for Medical Biotechnology, Faculty of Biology, University Duisburg-Essen, Universitätsstraße, Essen, Germany
| | - Anastassis Perrakis
- Department of Biochemistry, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Geert Jpl Kops
- Oncode Institute, Hubrecht Institute-KNAW and University Medical Center Utrecht, Utrecht, The Netherlands.
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8
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Abstract
BACKGROUND Bovine tuberculosis (bTB) remains a public health threat in low-income countries. Data on human tuberculosis (TB) due to Mycobacterium bovis are poorly documented in developing countries. AIMS To determine the occurrence of active pulmonary TB due to M. bovis in abattoir workers, butchers, livestock farmers and veterinarians and to document their knowledge and practices regarding bTB. METHODS A cross-sectional study of abattoir workers, butchers, livestock farmers, veterinary doctors and veterinary assistants, which obtained data on socio-demographic conditions, knowledge and practices regarding TB. Sputum samples were collected from respondents with a chronic cough. The chi-squared test was used for statistical analysis. RESULTS A total of 141 abattoir workers, 317 butchers, 50 livestock farmers, five veterinary doctors and three veterinary assistants took part. Four out of 16 abattoir workers and 1 out of 50 livestock farmers were positive for M. bovis by PCR analysis. Duration of work as an abattoir worker was significantly associated (P < 0.05) with prevalence of zoonotic TB. The knowledge of abattoir workers, butchers, livestock farmers and veterinary assistants regarding transmission of bTB from animals to humans and the symptoms of TB in humans was very poor. Most of these workers did not use protective equipment and appropriate safe working techniques and were considered at high risk of acquiring zoonotic TB. CONCLUSIONS Zoonotic TB is a significant public health issue among professionally exposed groups in Peshawar, Pakistan and suggests a need for further detailed investigations of the disease in this and similar areas.
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Affiliation(s)
- I Khattak
- Department of Epidemiology and Public Health, University of Veterinary and Animal Sciences, Lahore 5400, Pakistan,
| | - M H Mushtaq
- Department of Epidemiology and Public Health, University of Veterinary and Animal Sciences, Lahore 5400, Pakistan
| | - M U D Ahmad
- Department of Epidemiology and Public Health, University of Veterinary and Animal Sciences, Lahore 5400, Pakistan
| | - M S Khan
- Department of Clinical Medicine and Surgery, University of Veterinary and Animal Sciences, Lahore 5400, Pakistan
| | - J Haider
- Center for Biotechnology and Microbiology, University of Swat, Swat 19200, Pakistan
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9
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Ahmad MUD, Waege I, Hausner W, Thomm M, Boos W, Diederichs K, Welte W. Structural Insights into Nonspecific Binding of DNA by TrmBL2, an Archaeal Chromatin Protein. J Mol Biol 2015; 427:3216-3229. [PMID: 26299937 DOI: 10.1016/j.jmb.2015.08.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Revised: 08/04/2015] [Accepted: 08/10/2015] [Indexed: 10/23/2022]
Abstract
The crystal structure of TrmBL2 from the archaeon Pyrococcus furiosus shows an association of two pseudosymmetric dimers. The dimers follow the prototypical design of known bacterial repressors with two helix-turn-helix (HTH) domains binding to successive major grooves of the DNA. However, in TrmBL2, the two dimers are arranged at a mutual displacement of approximately 2bp so that they associate with the DNA along the double-helical axis at an angle of approximately 80°. While the deoxyribose phosphate groups of the double-stranded DNA (dsDNA) used for co-crystallization are clearly seen in the electron density map, most of the nucleobases are averaged out. Refinement required to assume a superposition of at least three mutually displaced dsDNAs. The HTH domains interact primarily with the deoxyribose phosphate groups and polar interactions with the nucleobases are almost absent. This hitherto unseen mode of DNA binding by TrmBL2 seems to arise from nonoptimal protein-DNA contacts made by its four HTH domains resulting in a low-affinity, nonspecific binding to DNA.
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Affiliation(s)
- Misbha Ud Din Ahmad
- University of Konstanz Department of Biology, Universitätsstrasse 10, 78456 Konstanz, Germany
| | - Ingrid Waege
- University Regensburg Lehrstuhl für Mikrobiologie, Universitätsstrasse 31, 93053 Regensburg, Germany
| | - Winfried Hausner
- University Regensburg Lehrstuhl für Mikrobiologie, Universitätsstrasse 31, 93053 Regensburg, Germany
| | - Michael Thomm
- University Regensburg Lehrstuhl für Mikrobiologie, Universitätsstrasse 31, 93053 Regensburg, Germany
| | - Winfried Boos
- University of Konstanz Department of Biology, Universitätsstrasse 10, 78456 Konstanz, Germany
| | - Kay Diederichs
- University of Konstanz Department of Biology, Universitätsstrasse 10, 78456 Konstanz, Germany
| | - Wolfram Welte
- University of Konstanz Department of Biology, Universitätsstrasse 10, 78456 Konstanz, Germany.
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