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Borne R, Vita N, Franche N, Tardif C, Perret S, Fierobe HP. Engineering of a new Escherichia coli strain efficiently metabolizing cellobiose with promising perspectives for plant biomass-based application design. Metab Eng Commun 2021; 12:e00157. [PMID: 33457204 PMCID: PMC7797564 DOI: 10.1016/j.mec.2020.e00157] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Revised: 11/24/2020] [Accepted: 12/14/2020] [Indexed: 11/30/2022] Open
Abstract
The necessity to decrease our fossil energy dependence requests bioprocesses based on biomass degradation. Cellobiose is the main product released by cellulases when acting on the major plant cell wall polysaccharide constituent, the cellulose. Escherichia coli, one of the most common model organisms for the academy and the industry, is unable to metabolize this disaccharide. In this context, the remodeling of E. coli to catabolize cellobiose should thus constitute an important progress for the design of such applications. Here, we developed a robust E. coli strain able to metabolize cellobiose by integration of a small set of modifications in its genome. Contrary to previous studies that use adaptative evolution to achieve some growth on this sugar by reactivating E. coli cryptic operons coding for cellobiose metabolism, we identified easily insertable modifications impacting the cellobiose import (expression of a gene coding a truncated variant of the maltoporin LamB, modification of the expression of lacY encoding the lactose permease) and its intracellular degradation (genomic insertion of a gene encoding either a cytosolic β-glucosidase or a cellobiose phosphorylase). Taken together, our results provide an easily transferable set of mutations that confers to E. coli an efficient growth phenotype on cellobiose (doubling time of 2.2 h in aerobiosis) without any prior adaptation. Production of a cytosolic β-glucosidase or cellobiose phosphorylase allows E. coli to metabolize cellobiose. Optimization of cellobiose uptake through E. coli enveloppe to sustain an efficient growth on this carbon source. Genetic engineering of E. coli can provide the capacity of an efficient cellobiose catabolism.
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Affiliation(s)
- Romain Borne
- Aix-Marseille Université, CNRS, UMR7283, 31 ch. Joseph Aiguier, F-13402, Marseille, France
| | - Nicolas Vita
- Aix-Marseille Université, CNRS, UMR7283, 31 ch. Joseph Aiguier, F-13402, Marseille, France
| | - Nathalie Franche
- Aix-Marseille Université, CNRS, UMR7283, 31 ch. Joseph Aiguier, F-13402, Marseille, France
| | - Chantal Tardif
- Aix-Marseille Université, CNRS, UMR7283, 31 ch. Joseph Aiguier, F-13402, Marseille, France
| | - Stéphanie Perret
- Aix-Marseille Université, CNRS, UMR7283, 31 ch. Joseph Aiguier, F-13402, Marseille, France
| | - Henri-Pierre Fierobe
- Aix-Marseille Université, CNRS, UMR7283, 31 ch. Joseph Aiguier, F-13402, Marseille, France
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2
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Endutkin AV, Yudkina AV, Sidorenko VS, Zharkov DO. Transient protein-protein complexes in base excision repair. J Biomol Struct Dyn 2018; 37:4407-4418. [PMID: 30488779 DOI: 10.1080/07391102.2018.1553741] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Transient protein-protein complexes are of great importance for organizing multiple enzymatic reactions into productive reaction pathways. Base excision repair (BER), a process of critical importance for maintaining genome stability against a plethora of DNA-damaging factors, involves several enzymes, including DNA glycosylases, AP endonucleases, DNA polymerases, DNA ligases and accessory proteins acting sequentially on the same damaged site in DNA. Rather than being assembled into one stable multisubunit complex, these enzymes pass the repair intermediates between them in a highly coordinated manner. In this review, we discuss the nature and the role of transient complexes arising during BER as deduced from structural and kinetic data. Almost all of the transient complexes are DNA-mediated, although some may also exist in solution and strengthen under specific conditions. The best-studied example, the interactions between DNA glycosylases and AP endonucleases, is discussed in more detail to provide a framework for distinguishing between stable and transient complexes based on the kinetic data. Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Anton V Endutkin
- SB RAS Institute of Chemical Biology and Fundamental Medicine , Novosibirsk , Russia.,Novosibirsk State University , Novosibirsk , Russia.,Podalirius Ltd. , Novosibirsk , Russia
| | - Anna V Yudkina
- SB RAS Institute of Chemical Biology and Fundamental Medicine , Novosibirsk , Russia.,Novosibirsk State University , Novosibirsk , Russia
| | - Viktoriya S Sidorenko
- Department of Pharmacological Sciences, Stony Brook University , Stony Brook , NY , USA
| | - Dmitry O Zharkov
- SB RAS Institute of Chemical Biology and Fundamental Medicine , Novosibirsk , Russia.,Novosibirsk State University , Novosibirsk , Russia
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3
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Sousa FL, Parente DJ, Hessman JA, Chazelle A, Teichmann SA, Swint-Kruse L. Data on publications, structural analyses, and queries used to build and utilize the AlloRep database. Data Brief 2016; 8:948-57. [PMID: 27508249 PMCID: PMC4961497 DOI: 10.1016/j.dib.2016.07.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Revised: 06/22/2016] [Accepted: 07/04/2016] [Indexed: 01/08/2023] Open
Abstract
The AlloRep database (www.AlloRep.org) (Sousa et al., 2016) [1] compiles extensive sequence, mutagenesis, and structural information for the LacI/GalR family of transcription regulators. Sequence alignments are presented for >3000 proteins in 45 paralog subfamilies and as a subsampled alignment of the whole family. Phenotypic and biochemical data on almost 6000 mutants have been compiled from an exhaustive search of the literature; citations for these data are included herein. These data include information about oligomerization state, stability, DNA binding and allosteric regulation. Protein structural data for 65 proteins are presented as easily-accessible, residue-contact networks. Finally, this article includes example queries to enable the use of the AlloRep database. See the related article, “AlloRep: a repository of sequence, structural and mutagenesis data for the LacI/GalR transcription regulators” (Sousa et al., 2016) [1].
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Affiliation(s)
- Filipa L Sousa
- Institute of Molecular Evolution, Heinrich-Heine Universität Düsseldorf, Universitätstrasse 1, 40225 Düsseldorf, Germany
| | - Daniel J Parente
- The Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS 66160, USA
| | - Jacob A Hessman
- The Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS 66160, USA
| | - Allen Chazelle
- The Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS 66160, USA
| | - Sarah A Teichmann
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SD, UK; Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SA, UK
| | - Liskin Swint-Kruse
- The Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, KS 66160, USA
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4
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Abstract
Rapid development of genomic and proteomic methodologies has provided a wealth of data for deciphering the biomolecular circuitry of a living cell. The main areas of computational research of proteomes outlined in this review are: understanding the system, its features and parameters to help plan the experiments; data integration, to help produce more reliable data sets; visualization and other forms of data representation to simplify interpretation; modeling of the functional regulation; and systems biology. With false-positive rates reaching 50% even in the more reliable data sets, handling the experimental error remains one of the most challenging tasks. Integrative approaches, incorporating results of various genome- and proteome-wide experiments, allow for minimizing the error and bring with them significant predictive power.
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5
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Abstract
Regulatory DNAs serve as templates to bring weakly interacting transcription factors into close proximity so they can work synergistically to switch genes on and off in time and space. Most of these regulatory DNAs are enhancers that can work over long distances--a million base pairs or more in mammals--to control gene expression. Critical enhancers are sometimes even found within the introns of neighboring genes. This review summarizes well-defined examples of enhancers controlling key processes in animal development. Potential mechanisms of transcriptional synergy are discussed with regard to enhancer structure and contemporary ChIP-sequencing assays, whereby just a small fraction of the observed binding sites represent bona fide regulatory DNAs. Finally, there is a discussion of how enhancer evolution can produce novelty in animal morphology and of the prospects for reconstructing transitions in animal evolution by introducing derived enhancers in basal ancestors.
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Affiliation(s)
- Mike Levine
- Department of Molecular and Cell Biology, University of California-Berkeley, CA 94720, USA.
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6
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Dawid A, Kiviet DJ, Kogenaru M, de Vos M, Tans SJ. Multiple peaks and reciprocal sign epistasis in an empirically determined genotype-phenotype landscape. CHAOS (WOODBURY, N.Y.) 2010; 20:026105. [PMID: 20590334 DOI: 10.1063/1.3453602] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Insight into the ruggedness of adaptive landscapes is central to understanding the mechanisms and constraints that shape the course of evolution. While empirical data on adaptive landscapes remain scarce, a handful of recent investigations have revealed genotype-phenotype and genotype-fitness landscapes that appeared smooth and single peaked. Here, we used existing in vivo measurements on lac repressor and operator mutants in Escherichia coli to reconstruct the genotype-phenotype map that details the repression value of this regulatory system as a function of two key repressor residues and four key operator base pairs. We found that this landscape is multipeaked, harboring in total 19 distinct optima. Analysis showed that all direct evolutionary pathways between peaks involve significant dips in the repression value. Consistent with earlier predictions, we found reciprocal sign epistatic interactions at the repression minimum of the most favorable paths between two peaks. These results suggest that the occurrence of multiple peaks and reciprocal epistatic interactions may be a general feature in coevolving systems like the repressor-operator pair studied here.
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Affiliation(s)
- Alexandre Dawid
- AMOLF Institute, Science Park 104, 1098 XG Amsterdam, The Netherlands
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7
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Han Y, You G, Pattenden LK, Forde GM. The harnessing of peptide–monolith constructs for single step plasmid DNA purification. Process Biochem 2010. [DOI: 10.1016/j.procbio.2009.09.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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8
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Oehler S, Müller-Hill B. High local concentration: a fundamental strategy of life. J Mol Biol 2009; 395:242-53. [PMID: 19883663 DOI: 10.1016/j.jmb.2009.10.056] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2009] [Revised: 10/22/2009] [Accepted: 10/27/2009] [Indexed: 12/26/2022]
Abstract
Local increase in concentration is a basic principle of transcriptional control. Closer inspection reveals that it is a major force governing all interactions within and between proteins and DNA. Local increase in concentration acts on all levels of organization of living matter. The structures and functions of two central molecules of life-the linear polymers DNA and protein-are particularly illuminating examples. Local increase in concentration leads to cooperative or competitive interactions between molecules. It is an important principle of life.
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Affiliation(s)
- Stefan Oehler
- Biomedical Sciences Research Center Alexander Fleming, 34 Fleming Street, GR-16672 Vari, Greece.
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9
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Han Y, Gras S, Forde GM. Binding properties of peptidic affinity ligands for plasmid DNA capture and detection. AIChE J 2009. [DOI: 10.1002/aic.11690] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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10
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Zharkov DO, Grollman AP. The DNA trackwalkers: principles of lesion search and recognition by DNA glycosylases. Mutat Res 2005; 577:24-54. [PMID: 15939442 DOI: 10.1016/j.mrfmmm.2005.03.011] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2005] [Revised: 03/28/2005] [Accepted: 03/29/2005] [Indexed: 11/24/2022]
Abstract
DNA glycosylases, the pivotal enzymes in base excision repair, are faced with the difficult task of recognizing their substrates in a large excess of unmodified DNA. We present here a kinetic analysis of DNA glycosylase substrate specificity, based on the probability of error. This novel approach to this subject explains many features of DNA surveillance and catalysis of lesion excision by DNA glycosylases. This approach also is applicable to the general issue of substrate specificity. We discuss determinants of substrate specificity in damaged DNA and in the enzyme, as well as methods by which these determinants can be identified.
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Affiliation(s)
- Dmitry O Zharkov
- Laboratory of Repair Enzymes, SB RAS Institute of Chemical Biology and Fundamental Medicine, Novosibirsk 630090, Russia.
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11
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Lewis M. The lac repressor. C R Biol 2005; 328:521-48. [PMID: 15950160 DOI: 10.1016/j.crvi.2005.04.004] [Citation(s) in RCA: 174] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2005] [Revised: 03/26/2005] [Accepted: 04/11/2005] [Indexed: 11/18/2022]
Abstract
Few proteins have had such a strong impact on a field as the lac repressor has had in Molecular Biology. Over 40 years ago, Jacob and Monod [Genetic regulatory mechanisms in the synthesis of proteins, J. Mol. Biol. 3 (1961) 318] proposed a model for gene regulation, which survives essentially unchanged in contemporary textbooks. It is a cogent depiction of how a set of 'structural' genes may be coordinately transcribed in response to environmental conditions and regulates metabolic events in the cell. In bacteria, the genes required for lactose utilization are negatively regulated when a repressor molecule binds to an upstream cis activated operator. The repressor and its operator together form a genetic switch, the lac operon. The switch functions when inducer molecules alter the conformation of the repressor in a specific manner. In the presence of a particular metabolite, the repressor undergoes a conformational change that reduces its affinity for the operator. The structures of the lac repressor and its complexes with operator DNA and effector molecules have provided a physical platform for visualizing at the molecular level the different conformations the repressor and the molecular basis for the switch. The structures of lac repressor, bound to its operator and inducer, have also been invaluable for interpreting a plethora of biochemical and genetic data.
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Affiliation(s)
- Mitchell Lewis
- School of Medicine, University of Pennsylvania, 813 Stellar-Chance Building, Philadelphia, PA 19104-6059, USA
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12
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Abstract
The use of plasmid DNA in gene therapy and genetic vaccination has increased the need for scalable and sustainable production processes. One key challenge for bioprocess engineering is the separation of plasmid DNA from structurally related impurities. Affinity purification procedures allow a highly selective capturing of the target molecule. In this paper, we present the isolation of a his-tagged lac repressor, its non-covalent immobilisation to different matrices and binding of DNA, thus enabling us to screen for combinations of ligands and stationary phases by using a building block principle.
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Affiliation(s)
- Anja Hasche
- Department of Fermentation Engineering, Faculty of Technology, Bielefeld University, Universitaetsstrasse 25, P.O. Box 100131, D-33501 Bielefeld, Germany
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13
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Semsey S, Tolstorukov MY, Virnik K, Zhurkin VB, Adhya S. DNA trajectory in the Gal repressosome. Genes Dev 2004; 18:1898-907. [PMID: 15289461 PMCID: PMC517409 DOI: 10.1101/gad.1209404] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2004] [Accepted: 05/25/2004] [Indexed: 11/24/2022]
Abstract
The Gal repressosome is a higher-order nucleoprotein complex that represses transcription of the gal operon in Escherichia coli. During the repressosome assembly, a DNA loop is formed by the interaction of two GalR dimers, bound to two spatially separated operators, OE and OI, flanking the gal promoters. Structure-based genetic analysis indicated that GalR homodimers interact directly and form a V-shaped stacked tetramer in repressosome, further stabilized by HU binding to an architecturally critical position on the DNA. In this scheme of GalR tetramerization, the alignment of the operators in the DNA loop could be in either parallel (PL) or antiparallel (AL) mode. As each mode can have two alternative geometries differing in the mutual stacking of the OE- and OI-bound GalR dimers, it is possible to have four different DNA trajectories in the repressosome. Feasibilities of these trajectories were tested by in vitro transcription repression assays, first by isolating GalR mutants with altered operator specificity and then by constructing four different potential loops with mutant GalR heterodimers bound to specifically designed hybrid operators in such a way as to give rise to only one of the four putative trajectories. Results show that OE and OI adopt a mutual antiparallel orientation in an under-twisted DNA loop, consistent with the energetically optimal structural model. In this structure the center of the HU-binding site is located at the apex of the DNA loop. The approach reported here can be used to distinguish between otherwise indistinguishable DNA trajectories in complex nucleoprotein machines.
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Affiliation(s)
- Szabolcs Semsey
- Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
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14
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Grigoriev A. A relationship between gene expression and protein interactions on the proteome scale: analysis of the bacteriophage T7 and the yeast Saccharomyces cerevisiae. Nucleic Acids Res 2001; 29:3513-9. [PMID: 11522820 PMCID: PMC55876 DOI: 10.1093/nar/29.17.3513] [Citation(s) in RCA: 179] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The relationship between the similarity of expression patterns for a pair of genes and interaction of the proteins they encode is demonstrated both for the simple genome of the bacteriophage T7 and the considerably more complex genome of the yeast Saccharomyces cerevisiae. Statistical analysis of large-scale gene expression and protein interaction data shows that protein pairs encoded by co-expressed genes interact with each other more frequently than with random proteins. Furthermore, the mean similarity of expression profiles is significantly higher for respective interacting protein pairs than for random ones. Such coupled analysis of gene expression and protein interaction data may allow evaluation of the results of large-scale gene expression and protein interaction screens as demonstrated for several publicly available datasets. The role of this link between expression and interaction in the evolution from monomeric to oligomeric protein structures is also discussed.
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Affiliation(s)
- A Grigoriev
- GPC Biotech, Fraunhoferstrasse 20, Martinsried 82152, Germany.
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15
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Bontidean I, Kumar A, Csöregi E, Galaev IY, Mattiasson B. Highly Sensitive Novel Biosensor Based on an Immobilizedlac Repressor. Angew Chem Int Ed Engl 2001. [DOI: 10.1002/1521-3757(20010716)113:14<2748::aid-ange2748>3.0.co;2-w] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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16
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Bontidean I, Kumar A, Csöregi E, Galaev IY, Mattiasson B. Highly Sensitive Novel Biosensor Based on an Immobilizedlac Repressor. Angew Chem Int Ed Engl 2001; 40:2676-2678. [DOI: 10.1002/1521-3773(20010716)40:14<2676::aid-anie2676>3.0.co;2-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2001] [Indexed: 11/07/2022]
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17
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Hart DJ, Speight RE, Sutherland JD, Blackburn JM. Analysis of the NF-kappaB p50 dimer interface by diversity screening. J Mol Biol 2001; 310:563-75. [PMID: 11439024 DOI: 10.1006/jmbi.2001.4724] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
An in vivo screen has been devised for NF-kappaB p50 activity in Escherichia coli exploiting the ability of the mammalian transcription factor to emulate a prokaryotic repressor. Active intracellular p50 was shown to repress the expression of a green fluorescent protein reporter gene allowing for visual screening of colonies expressing active p50 on agar plates. A library of mutants was constructed in which the residues Y267, L269, A308 and V310 of the dimer interface were simultaneously randomised and twenty-five novel functional interfaces were selected which repressed the reporter gene to similar levels as the wild-type protein. The leucine-269 alanine-308 core was repeatedly, but not exclusively, selected from the library whilst a diversity of predominantly non-polar residues were selected at positions 267 and 310. These results indicate that L269 and A308 may form a hot spot of interaction and allow an insight into the processes of dimer selectivity and evolution within this family of transcription factors.
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Affiliation(s)
- D J Hart
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QW, UK
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18
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Gerk LP, Leven O, Müller-Hill B. Strengthening the dimerisation interface of Lac repressor increases its thermostability by 40 deg. C. J Mol Biol 2000; 299:805-12. [PMID: 10835285 DOI: 10.1006/jmbi.2000.3706] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We increased drastically the heat stability of Lac repressor (LacR) of Escherichia coli. Wild-type tetrameric LacR denatures irreversibly at 53 degrees C. Improving hydrophobic packing at the dimerisation interface by a single substitution increases LacR heat-resistance by 40 deg. C without abolishing inducer binding at high and low temperatures. Tetrameric LacR mutants carrying substitutions of the positively charged amino acid Lys84 by each of the hydrophobic amino acids Leu, Ile and Met resist heating to temperatures up to 93 degrees C. We performed IPTG binding assays at 80 degrees C and found the mutant Lac repressors active and, thus, the core intact. Furthermore, the activity of LacR following heating is shown at room temperature by a gel retardation assay, which demonstrates normal oligomerisation state and function of the headpiece. The same mutations (K84L/I/M) in the dimer LacR331stop, carrying a stop codon in amino acid 331, increase thermostability of the dimer from 47 degrees C to 87 degrees C. LacRK84M represses beta-galactosidase activity in vivo as well as the wild-type and is sufficiently induced to allow growth on lactose. The results with both tetramer and dimer variants of LacR indicate mutual stabilisation of the tetramerisation region and the stable core.
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Affiliation(s)
- L P Gerk
- Institut für Genetik, Universität zu Köln, Köln, Weyertal 121, 50931, Germany. Lily.pereg.gerk.com
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19
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Dong F, Spott S, Zimmermann O, Kisters-Woike B, Müller-Hill B, Barker A. Dimerisation mutants of Lac repressor. I. A monomeric mutant, L251A, that binds Lac operator DNA as a dimer. J Mol Biol 1999; 290:653-66. [PMID: 10395821 DOI: 10.1006/jmbi.1999.2902] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Dimer formation between monomers of the Escherichia coli Lac repressor is substantially specificed by the interactions between three alpha-helices in each monomer which form a hydrophobic interface. As a first step in analysing the specificity of this interaction, we examined the mutant L251A. LacR bearing this mutation in a background lacking the C-terminal heptad repeats is completely incapable of forming dimers in solution, with a dimer-monomer equilibrium dissociation constant, or Kd, higher than 10(-5)M. This correlates with a 200-fold decrease in its ability to repress the lac operon in vivo compared to dimeric LacR. Surprisingly, the mutant is still capable of forming dimers upon binding to short operator DNA in vitro. Analysis of the kinetic parameters of binding of the mutant to operator DNA reveals a 2000 to 3000-fold increase in the equilibrium dissociation constant (Kd) of the mutant-DNA complex in comparison to dimeric LacR-operator complexes, with the change almost entirely due to a greater than 1000-fold decrease in association rate. The dissociation rate varies only by a factor of about two, in comparison to dimeric LacR. This change reflects a kinetic pathway in which dimer formation, in solution or on DNA, is the rate-limiting step. These findings have implications for the specificity and stability of the protein-protein interface in question.
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Affiliation(s)
- F Dong
- Institut für Genetik der Universität zu Köln, Köln, Weyertal 121, 50931, Germany
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20
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Oehler S, Alex R, Barker A. Is nitrocellulose filter binding really a universal assay for protein-DNA interactions? Anal Biochem 1999; 268:330-6. [PMID: 10075823 DOI: 10.1006/abio.1998.3056] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The ability to bind to nitrocellulose is commonly accepted as being a universal property of proteins and has been widely used in many different fields of study. This property was first exploited in the study of DNA-binding proteins 30 years ago, in studies involving DNA binding by the lactose repressor (LacR) of Escherichia coli. Termed the filter-binding assay, it remains the quickest and easiest assay available for the study of protein-DNA interactions. However, the exact mechanism by which proteins bind to nitrocellulose remains uncertain. Given the supposedly universal nature of the interaction, we were surprised to notice that certain LacR variants were completely unable to bind simultaneously to DNA containing a single lac operator and nitrocellulose. Investigation of this loss of binding suggests that LacR requires a protein region that is both hydrophobic in nature and more or less unstructured, in order to bind to both nitrocellulose and DNA. In the case of wild-type, tetrameric LacR, the DNA-recognition domain that is not bound to DNA suffices. Dimeric LacR variants will only bind if they have certain C-terminal extensions. These experiments sound a cautionary note for the use of filter binding as an assay of choice, particularly in applications involving screening for the DNA-binding site of putative DNA-binding proteins.
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Affiliation(s)
- S Oehler
- Institut für Genetik der Universität zu Köln, Weyertal 121, Köln, 50931, Germany
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