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Lü H, Wang J. Annotation of signal transduction systems in living bacteria by monitoring the TF-promotor binding <italic>in situ</italic> based on intermolecular FRET. CHINESE SCIENCE BULLETIN-CHINESE 2022. [DOI: 10.1360/tb-2022-0952] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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2
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Wang P, Zhang G, Xu Z, Chen Z, Liu X, Wang C, Zheng C, Wang J, Zhang H, Yan A. Whole-cell FRET monitoring of transcription factor activities enables functional annotation of signal transduction systems in living bacteria. J Biol Chem 2022; 298:102258. [PMID: 35839853 PMCID: PMC9396075 DOI: 10.1016/j.jbc.2022.102258] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2022] [Revised: 06/29/2022] [Accepted: 07/01/2022] [Indexed: 11/24/2022] Open
Abstract
Bacteria adapt to their constantly changing environments largely by transcriptional regulation through the activities of various transcription factors (TFs). However, techniques that monitor TF–promoter interactions in situ in living bacteria are lacking. Herein, we developed a whole-cell TF–promoter binding assay based on the intermolecular FRET between an unnatural amino acid, l-(7-hydroxycoumarin-4-yl) ethylglycine, which labels TFs with bright fluorescence through genetic encoding (donor fluorophore) and the live cell nucleic acid stain SYTO 9 (acceptor fluorophore). We show that this new FRET pair monitors the intricate TF–promoter interactions elicited by various types of signal transduction systems, including one-component (CueR) and two-component systems (BasSR and PhoPQ), in bacteria with high specificity and sensitivity. We demonstrate that robust CouA incorporation and FRET occurrence is achieved in all these regulatory systems based on either the crystal structures of TFs or their simulated structures, if 3D structures of the TFs were unavailable. Furthermore, using CueR and PhoPQ systems as models, we demonstrate that the whole-cell FRET assay is applicable for the identification and validation of complex regulatory circuit and novel modulators of regulatory systems of interest. Finally, we show that the FRET system is applicable for single-cell analysis and monitoring TF activities in Escherichia coli colonizing a Caenorhabditis elegans host. In conclusion, we established a tractable and sensitive TF–promoter binding assay, which not only complements currently available approaches for DNA–protein interactions but also provides novel opportunities for functional annotation of bacterial signal transduction systems and studies of the bacteria–host interface.
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Affiliation(s)
- Pengchao Wang
- School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China; Department of Biology, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, Guangdong, China
| | - Guangming Zhang
- School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China
| | - Zeling Xu
- School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China
| | - Zhe Chen
- School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China
| | - Xiaohong Liu
- Institute of Biophysics, Chinese Academy of Sciences, Beijing, 15 Datun Road, Chaoyang District, Beijing 100101, China
| | - Chenyin Wang
- School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China
| | - Chaogu Zheng
- School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China
| | - Jiangyun Wang
- Institute of Biophysics, Chinese Academy of Sciences, Beijing, 15 Datun Road, Chaoyang District, Beijing 100101, China.
| | - Hongmin Zhang
- Department of Biology, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, Guangdong, China.
| | - Aixin Yan
- School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China.
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Boyle EA, Becker WR, Bai HB, Chen JS, Doudna JA, Greenleaf WJ. Quantification of Cas9 binding and cleavage across diverse guide sequences maps landscapes of target engagement. SCIENCE ADVANCES 2021; 7:7/8/eabe5496. [PMID: 33608277 PMCID: PMC7895440 DOI: 10.1126/sciadv.abe5496] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Accepted: 01/07/2021] [Indexed: 06/12/2023]
Abstract
The RNA-guided nuclease Cas9 has unlocked powerful methods for perturbing both the genome through targeted DNA cleavage and the regulome through targeted DNA binding, but limited biochemical data have hampered efforts to quantitatively model sequence perturbation of target binding and cleavage across diverse guide sequences. We present scalable, sequencing-based platforms for high-throughput filter binding and cleavage and then perform 62,444 quantitative binding and cleavage assays on 35,047 on- and off-target DNA sequences across 90 Cas9 ribonucleoproteins (RNPs) loaded with distinct guide RNAs. We observe that binding and cleavage efficacy, as well as specificity, vary substantially across RNPs; canonically studied guides often have atypically high specificity; sequence context surrounding the target modulates Cas9 on-rate; and Cas9 RNPs may sequester targets in nonproductive states that contribute to "proofreading" capability. Lastly, we distill our findings into an interpretable biophysical model that predicts changes in binding and cleavage for diverse target sequence perturbations.
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Affiliation(s)
- Evan A Boyle
- Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305, USA.
| | - Winston R Becker
- Program in Biophysics, Stanford University, Stanford, CA 94305, USA
| | - Hua B Bai
- Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Janice S Chen
- Department of Molecular and Cell Biology, California Institute for Quantitative Biosciences (QB3), University of California, Howard Hughes Medical Institute, Department of Chemistry, and the Innovative Genomics Institute, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Jennifer A Doudna
- Department of Molecular and Cell Biology, California Institute for Quantitative Biosciences (QB3), University of California, Howard Hughes Medical Institute, Department of Chemistry, and the Innovative Genomics Institute, University of California, Berkeley, Berkeley, CA 94720, USA
- MBIB Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94710, USA
- Gladstone Institutes, University of California, San Francisco, San Francisco, CA 94158, USA
| | - William J Greenleaf
- Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305, USA.
- Department of Applied Physics, Stanford University, Stanford, CA 94305, USA
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4
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Weeramange CJ, Fairlamb MS, Singh D, Fenton AW, Swint‐Kruse L. The strengths and limitations of using biolayer interferometry to monitor equilibrium titrations of biomolecules. Protein Sci 2020; 29:1018-1034. [PMID: 31943488 PMCID: PMC7096710 DOI: 10.1002/pro.3827] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 01/03/2020] [Accepted: 01/08/2020] [Indexed: 12/13/2022]
Abstract
Every method used to quantify biomolecular interactions has its own strengths and limitations. To quantify protein-DNA binding affinities, nitrocellulose filter binding assays with 32 P-labeled DNA quantify Kd values from 10-12 to 10-8 M but have several technical limitations. Here, we considered the suitability of biolayer interferometry (BLI), which monitors association and dissociation of a soluble macromolecule to an immobilized species; the ratio koff /kon determines Kd . However, for lactose repressor protein (LacI) and an engineered repressor protein ("LLhF") binding immobilized DNA, complicated kinetic curves precluded this analysis. Thus, we determined whether the amplitude of the BLI signal at equilibrium related linearly to the fraction of protein bound to DNA. A key question was the effective concentration of immobilized DNA. Equilibrium titration experiments with DNA concentrations below Kd (equilibrium binding regime) must be analyzed differently than those with DNA near or above Kd (stoichiometric binding regime). For ForteBio streptavidin tips, the most frequent effective DNA concentration was ~2 × 10-9 M. Although variation occurred among different lots of sensor tips, binding events with Kd ≥ 10-8 M should reliably be in the equilibrium binding regime. We also observed effects from multi-valent interactions: Tetrameric LacI bound two immobilized DNAs whereas dimeric LLhF did not. We next used BLI to quantify the amount of inducer sugars required to allosterically diminish protein-DNA binding and to assess the affinity of fructose-1-kinase for the DNA-LLhF complex. Overall, when experimental design corresponded with appropriate data interpretation, BLI was convenient and reliable for monitoring equilibrium titrations and thereby quantifying a variety of binding interactions.
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Affiliation(s)
- Chamitha J. Weeramange
- Department of Biochemistry and Molecular BiologyThe University of Kansas Medical CenterKansas CityKansas
| | - Max S. Fairlamb
- Department of Biochemistry and Molecular BiologyThe University of Kansas Medical CenterKansas CityKansas
| | - Dipika Singh
- Department of Biochemistry and Molecular BiologyThe University of Kansas Medical CenterKansas CityKansas
| | - Aron W. Fenton
- Department of Biochemistry and Molecular BiologyThe University of Kansas Medical CenterKansas CityKansas
| | - Liskin Swint‐Kruse
- Department of Biochemistry and Molecular BiologyThe University of Kansas Medical CenterKansas CityKansas
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5
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Nithin C, Mukherjee S, Bahadur RP. A structure-based model for the prediction of protein-RNA binding affinity. RNA (NEW YORK, N.Y.) 2019; 25:1628-1645. [PMID: 31395671 PMCID: PMC6859855 DOI: 10.1261/rna.071779.119] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2019] [Accepted: 08/05/2019] [Indexed: 05/28/2023]
Abstract
Protein-RNA recognition is highly affinity-driven and regulates a wide array of cellular functions. In this study, we have curated a binding affinity data set of 40 protein-RNA complexes, for which at least one unbound partner is available in the docking benchmark. The data set covers a wide affinity range of eight orders of magnitude as well as four different structural classes. On average, we find the complexes with single-stranded RNA have the highest affinity, whereas the complexes with the duplex RNA have the lowest. Nevertheless, free energy gain upon binding is the highest for the complexes with ribosomal proteins and the lowest for the complexes with tRNA with an average of -5.7 cal/mol/Å2 in the entire data set. We train regression models to predict the binding affinity from the structural and physicochemical parameters of protein-RNA interfaces. The best fit model with the lowest maximum error is provided with three interface parameters: relative hydrophobicity, conformational change upon binding and relative hydration pattern. This model has been used for predicting the binding affinity on a test data set, generated using mutated structures of yeast aspartyl-tRNA synthetase, for which experimentally determined ΔG values of 40 mutations are available. The predicted ΔGempirical values highly correlate with the experimental observations. The data set provided in this study should be useful for further development of the binding affinity prediction methods. Moreover, the model developed in this study enhances our understanding on the structural basis of protein-RNA binding affinity and provides a platform to engineer protein-RNA interfaces with desired affinity.
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Affiliation(s)
- Chandran Nithin
- Computational Structural Biology Lab, Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
| | - Sunandan Mukherjee
- Computational Structural Biology Lab, Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
| | - Ranjit Prasad Bahadur
- Computational Structural Biology Lab, Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
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Mitkin NA, Korneev K, Gorbacheva AM, Kuprash DV. Relative Efficiency of Transcription Factor Binding to Allelic Variants of Regulatory Regions of Human Genes in Immunoprecipitation and Real-Time PCR. Mol Biol 2019. [DOI: 10.1134/s0026893319030117] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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7
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Litwin TR, Solà M, Holt IJ, Neuman KC. A robust assay to measure DNA topology-dependent protein binding affinity. Nucleic Acids Res 2014; 43:e43. [PMID: 25552413 PMCID: PMC4402506 DOI: 10.1093/nar/gku1381] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2014] [Accepted: 12/18/2014] [Indexed: 02/04/2023] Open
Abstract
DNA structure and topology pervasively influence aspects of DNA metabolism including replication, transcription and segregation. However, the effects of DNA topology on DNA-protein interactions have not been systematically explored due to limitations of standard affinity assays. We developed a method to measure protein binding affinity dependence on the topology (topological linking number) of supercoiled DNA. A defined range of DNA topoisomers at equilibrium with a DNA binding protein is separated into free and protein-bound DNA populations using standard nitrocellulose filter binding techniques. Electrophoretic separation and quantification of bound and free topoisomers combined with a simple normalization procedure provide the relative affinity of the protein for the DNA as a function of linking number. Employing this assay we measured topology-dependent DNA binding of a helicase, a type IB topoisomerase, a type IIA topoisomerase, a non-specific mitochondrial DNA binding protein and a type II restriction endonuclease. Most of the proteins preferentially bind negatively supercoiled DNA but the details of the topology-dependent affinity differ among proteins in ways that expose differences in their interactions with DNA. The topology-dependent binding assay provides a robust and easily implemented method to probe topological influences on DNA-protein interactions for a wide range of DNA binding proteins.
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Affiliation(s)
- Tamara R Litwin
- National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20814, USA Mitochondrial Biology Unit, Medical Research Council, Wellcome Trust/MRC Building, Hills Road, Cambridge, CB2 0XY, UK
| | - Maria Solà
- Department of Structural Biology, Molecular Biology Institute of Barcelona (CSIC), 08028 Barcelona, Spain
| | - Ian J Holt
- National Institute for Medical Research, Medical Research Council, The Ridgeway, Mill Hill, London, NW7 1AA, UK
| | - Keir C Neuman
- National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20814, USA
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8
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FRET-based analysis of protein-nucleic acid interactions by genetically incorporating a fluorescent amino acid. Amino Acids 2014; 47:729-34. [PMID: 25540052 DOI: 10.1007/s00726-014-1900-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2014] [Accepted: 12/12/2014] [Indexed: 10/24/2022]
Abstract
Protein-nucleic acid interaction is an important process in many biological phenomena. In this study, a fluorescence resonance energy transfer (FRET)-based protein-DNA binding assay has been developed, in which a fluorescent amino acid is genetically incorporated into a DNA-binding protein. A coumarin-containing amino acid was incorporated into a DNA-binding protein, and the mutant protein specifically produced a FRET signal upon binding to its cognate DNA labeled with a fluorophore. The protein-DNA binding affinity was then measured under equilibrium conditions. This method is advantageous for studying protein-nucleic acid interactions, because it is performed under equilibrium conditions, technically easy, and applicable to any nucleic acid-binding protein.
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9
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Kolitz S, Lorsch JR. Protein Filter Binding. Methods Enzymol 2014; 541:197-205. [DOI: 10.1016/b978-0-12-420119-4.00016-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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10
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Zhang X, Chabot D, Sultan Y, Monreal C, DeRosa MC. Target-molecule-triggered rupture of aptamer-encapsulated polyelectrolyte microcapsules. ACS APPLIED MATERIALS & INTERFACES 2013; 5:5500-5507. [PMID: 23756318 DOI: 10.1021/am400668q] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Polyelectrolyte microcapsules have great potential for serving as carriers for the delivery of their contents when triggered by an external stimulus. Aptamers are synthetic ssDNA or RNA that can bind to specific targets with high affinity and selectivity. Aptamers may retain these superior molecular recognition properties after encapsulation within polymer microcapsules. In this work, stable polyelectrolyte microcapsules with encapsulated aptamers were obtained by the layer-by-layer (LbL) method. Polyelectrolyte films were deposited onto a CaCO3 template that had been predoped with polystyrene sulfonate (PSS) and aptamer sequences (SA) that have an affinity for the dye sulforhodamine B (SRB). The PSS and aptamers are thought to serve as an internal scaffold supporting the microcapsule walls. These microcapsules would present target-molecule-triggered rupture properties. Microcapsule collapse was triggered by the binding of SRB to the encapsulated aptamer. The specificity of microcapsule collapse was investigated using a similar dye, tetramethylrosamine (TMR), which does not have affinity for SA. A high concentration of TMR did not lead to the collapse of the microcapsules. The effect of target binding on the microcapsules was confirmed by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). These microcapsules may have potential applications in targeted delivery systems for the controlled release of drugs, pesticides, or other payloads.
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Affiliation(s)
- Xueru Zhang
- Department of Chemistry, Carleton University, Ottawa, Canada
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11
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Low SC, Ahmad AL, Ideris N, Ng QH. Interaction of isothermal phase inversion and membrane formulation for pathogens detection in water. BIORESOURCE TECHNOLOGY 2012; 113:219-224. [PMID: 22153291 DOI: 10.1016/j.biortech.2011.11.048] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2011] [Revised: 11/11/2011] [Accepted: 11/11/2011] [Indexed: 05/31/2023]
Abstract
The aim of this study was to explore the utilization of polymeric membrane for bio-sensing application in most efficient and rapid way. Customization of membrane formulation via phase separation study to modify its morphologies and properties enable the detection of different pathogens in a specific manner. Experimental findings (FESEM, through-pore distribution, porosity, capillary flow test and protein binding test) verified the predictions of faster capillary flow time and higher membrane's protein binding by the addition of cellulose acetate and nitrocellulose to the membrane casting dope, respectively. Throughout the phase separation study, the potential phase behavior was investigated, which was correlating various membrane structures to its performances for potential pathogens detection in water.
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Affiliation(s)
- S C Low
- School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, Seri Ampangan, 14300 Nibong Tebal, S.P.S. Penang, Malaysia.
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12
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Moreau MJJ, Schaeffer PM. A polyplex qPCR-based binding assay for protein–DNA interactions. Analyst 2012; 137:4111-3. [DOI: 10.1039/c2an35703h] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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13
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Irvine EJ, Hernandez-Santana A, Faulds K, Graham D. Fabricating protein immunoassay arrays on nitrocellulose using dip-pen lithography techniques. Analyst 2011; 136:2925-30. [PMID: 21647488 DOI: 10.1039/c1an15178a] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Advancements in lithography methods for printing biomolecules on surfaces are proving to be potentially beneficial for disease screening and biological research. Dip-pen nanolithography (DPN) is a versatile micro and nanofabrication technique that has the ability to produce functional biomolecule arrays. The greatest advantage, with respect to the printing mechanism, is that DPN adheres to the sensitive mild conditions required for biomolecules such as proteins. We have developed an optimised, high-throughput printing technique for fabricating protein arrays using DPN. This study highlights the fabrication of a prostate specific antigen (PSA) immunoassay detectable by fluorescence. Spot sizes are typically no larger than 8 μm in diameter and limits of detection for PSA are comparable with a commercially available ELISA kit. Furthermore, atomic force microscopy (AFM) analysis of the array surface gives great insight into how the nitrocellulose substrate functions to retain protein integrity. This is the first report of protein arrays being printed on nitrocellulose using the DPN technique and the smallest feature size yet to be achieved on this type of surface. This method offers a significant advance in the ability to produce dense protein arrays on nitrocellulose which are suitable for disease screening using standard fluorescence detection.
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Affiliation(s)
- Eleanore Jane Irvine
- Centre for Nanometrology, Department of Pure and Applied Chemistry, WestCHEM, University of Strathclyde, 295 Cathedral Street, Glasgow, UK
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Jing M, Bowser MT. Methods for measuring aptamer-protein equilibria: a review. Anal Chim Acta 2011; 686:9-18. [PMID: 21237304 PMCID: PMC3026478 DOI: 10.1016/j.aca.2010.10.032] [Citation(s) in RCA: 141] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2010] [Revised: 10/20/2010] [Accepted: 10/21/2010] [Indexed: 12/11/2022]
Abstract
Aptamers are single stranded DNA or RNA molecules that have been selected using in vitro techniques to bind target molecules with high affinity and selectivity, rivaling antibodies in many ways. In order to use aptamers in research and clinical applications, a thorough understanding of aptamer-target binding is necessary. In this article, we review methods for assessing aptamer-protein binding using separation based techniques such as dialysis, ultrafiltration, gel and capillary electrophoresis, and HPLC; as well as mixture based techniques such as fluorescence intensity and anisotropy, UV-vis absorption and circular dichroism, surface plasmon resonance, and isothermal titration calorimetry. For each method the principle, range of application and important features, such as sample consumption, experimental time and complexity, are summarized and compared.
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Affiliation(s)
- Meng Jing
- University of Minnesota, Department of Chemistry, 207 Pleasant St. SE, Minneapolis, MN 55455-0431, USA
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15
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Maslon MM, Hrstka R, Vojtesek B, Hupp TR. A divergent substrate-binding loop within the pro-oncogenic protein anterior gradient-2 forms a docking site for Reptin. J Mol Biol 2010; 404:418-38. [PMID: 20888340 DOI: 10.1016/j.jmb.2010.09.035] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Revised: 09/15/2010] [Accepted: 09/15/2010] [Indexed: 11/18/2022]
Abstract
Anterior gradient-2 (AGR2) functions in a range of biological systems, including goblet cell formation, limb regeneration, inhibition of p53, and metastasis. There are no well-validated binding proteins for AGR2 protein despite the wealth of data implicating an important cellular function in vertebrates. The yeast two-hybrid system was used to isolate the ATP binding protein Reptin as an AGR2-interacting protein. AGR2 formed a stable complex in human cell lysates with Reptin, thus validating Reptin as an AGR2 binding protein in cells. Reptin was also shown to be overproduced in a panel of primary breast cancer biopsy specimens, relative to normal adjacent tissue from the same patient, suggesting a role in cancer growth in vivo. Mutations were made at the two ATP binding motifs in Reptin to evaluate the effects of ATP on Reptin-AGR2 complex stability. Loss-of-ATP binding mutations at the Walker A motif (K83A) or gain-of-ATP binding mutations at the Walker B motif (D299N) resulted in Reptin mutants with altered oligomerization, thermostability, and AGR2 binding properties. These data indicate that the two ATP binding motifs of Reptin play a role in regulating the stability of the AGR2-Reptin complex. The minimal region of AGR2 interacting with Reptin was localized using overlapping peptide libraries derived from the AGR2 protein sequence. The Reptin docking site was mapped to a divergent octapeptide loop in the AGR2 superfamily between amino acids 104 and 111. Mutations at codon Y104 or F111 in full-length AGR2 destabilized the binding of Reptin. These data highlight the existence of a protein docking motif on AGR2 and an ATP-regulated peptide-binding activity for Reptin. This knowledge has implications for isolating other AGR2-interacting proteins, for developing assays to isolate small molecules that target the Reptin ATP binding site, and for measuring the effects of the Reptin-AGR2 complex in cancer cell growth.
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Affiliation(s)
- Magdalena M Maslon
- Cancer Research UK p53 Signal Transduction Laboratories, Cell Signalling Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh EX4 2XR, Scotland, UK
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16
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Printed protein microarrays on unmodified plastic substrates. Anal Chim Acta 2010; 671:92-8. [DOI: 10.1016/j.aca.2010.05.008] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2010] [Revised: 05/03/2010] [Accepted: 05/05/2010] [Indexed: 11/23/2022]
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17
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Athanasopoulos V, Barker A, Yu D, Tan AHM, Srivastava M, Contreras N, Wang J, Lam KP, Brown SHJ, Goodnow CC, Dixon NE, Leedman PJ, Saint R, Vinuesa CG. The ROQUIN family of proteins localizes to stress granules via the ROQ domain and binds target mRNAs. FEBS J 2010; 277:2109-27. [PMID: 20412057 DOI: 10.1111/j.1742-4658.2010.07628.x] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Roquin is an E3 ubiquitin ligase with a poorly understood but essential role in preventing T-cell-mediated autoimmune disease and in microRNA-mediated repression of inducible costimulator (Icos) mRNA. Roquin and its mammalian paralogue membrane-associated nucleic acid binding protein (MNAB) define a protein family distinguished by an approximately 200 amino acid domain of unknown function, ROQ, that is highly conserved from mammals to invertebrates and is flanked by a RING-1 zinc finger and a CCCH zinc finger. Here we show that human, Drosophila and Caenorhabditis elegans Roquin and human MNAB localize to the cytoplasm and upon stress are concentrated in stress granules, where stalled mRNA translation complexes are stored. The ROQ domain is necessary and sufficient for localization to arsenite-induced stress granules and to induce these structures upon overexpression, and is required to trigger Icos mRNA decay. Gel-shift, SPR and footprinting studies show that an N-terminal fragment centred on the ROQ domain binds RNA from the Icos 3'-untranslated region comprising the minimal sequence for Roquin-mediated repression, adjacent to the miR-101 sequence complementarity. These findings identify Roquin as an RNA-binding protein and establish a specific function for the ROQ protein domain in mRNA homeostasis. Structured digital abstract * MINT-7711163: TIA-1 (uniprotkb:P31483) and Roquin (uniprotkb:Q4VGL6) colocalize (MI:0403) by fluorescence microscopy (MI:0416) * MINT-7711475: RLE-1 (uniprotkb:O45962) and TIA-1 (uniprotkb:P31483) colocalize (MI:0403) by fluorescence microscopy (MI:0416) * MINT-7711487: DmRoquin (uniprotkb:Q9VV48) and TIA-1 (uniprotkb:P31483) colocalize (MI:0403) by fluorescence microscopy (MI:0416) * MINT-7711447, MINT-7711460: MNAB (uniprotkb:Q9HBD1) and TIA-1 (uniprotkb:P31483) colocalize (MI:0403) by fluorescence microscopy (MI:0416) * MINT-7711176: eIF3 (uniprotkb:P55884) and Roquin (uniprotkb:Q4VGL6) colocalize (MI:0403) by fluorescence microscopy (MI:0416) * MINT-7711192: DCP1A (uniprotkb:Q9NPI6) and TIA-1 (uniprotkb:P31483) colocalize (MI:0403) by fluorescence microscopy (MI:0416).
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Abstract
Negative feedback regulation, mediated through repressor binding site O3, which overlaps the lacI gene, could explain the robustness of the weak expression of Lac repressor. Significant autorepression of Lac repressor has never been ruled out. In the work presented here, the degree of autoregulation of Lac repressor was determined. It is negligible.
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Abstract
Structural studies of DNA-protein complexes reveal networks of contacts between proteins and the phosphates, sugars and bases of DNA. Our understanding of these structures, especially at the usual level of resolution for complexes between proteins and DNA (1.5-3.0 A), is not sufficient to be able to infer directly the relative contributions of each contact to the overall binding energy. A range of biochemical methods have therefore been developed in order to probe the relative affinities of proteins for particular DNA target sites in vitro. Of these, one of the easiest and most widely used is nitrocellulose filter-binding. By exploiting the differential adsorption to nitrocellulose of proteins and peptides compared to nucleic acids, it is possible to prepare equilibrium mixtures of the proteins and nucleic acids of choice and estimate the amount of complex formation by rapid filtration. The concentration dependence of binding yields estimates of the equilibrium dissociation constant and trivial variations allow access to kinetic and thermodynamic data. The use of this technique is illustrated here using results from our experiments with the Escherichia coli methionine repressor, MetJ.
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Affiliation(s)
- Peter G Stockley
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, LS2 9JT, UK
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20
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Investigating protein-protein interactions by far-Westerns. ADVANCES IN BIOCHEMICAL ENGINEERING/BIOTECHNOLOGY 2008; 110:195-214. [PMID: 18219468 DOI: 10.1007/10_2007_090] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The identification of protein interaction partners can often elucidate the function of the protein under investigation based on the "guilty by association" concept. Furthermore, the binding event between two proteins can be used as a functional assay when no such assay is available. Despite the large number of advanced techniques that are currently available for studying protein-protein interactions, far-Westerns or blot overlays are still very commonly used in the average laboratory setting due to their powerfulness. This is due to the simplicity and clarity in the results that they produce. Here, the details and mechanics of far-Westerns are discussed to help the reader choose amongst the different variations that exist depending on the question being investigated and the materials available to them. Some examples involving unique questions are also discussed in order to educate the reader on the versatility of far-Westerns. Finally, a troubleshooting section provides the reader with an understanding of the common problems that can be encountered and how these problems can be circumvented.
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21
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Ahmad AL, Low SC, Shukor SRA, Ismail A. Synthesis and characterization of polymeric nitrocellulose membranes: Influence of additives and pore formers on the membrane morphology. J Appl Polym Sci 2008. [DOI: 10.1002/app.27592] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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22
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Ganesan M, Paithankar KR, Jagannadham MV, Sundaram CS, Murthy BS, Singh L. Characterization of novel DNA-binding proteins expressed in snake oocyte cDNA library. Protein Expr Purif 2007; 53:164-78. [PMID: 17189702 DOI: 10.1016/j.pep.2006.11.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2006] [Revised: 11/09/2006] [Accepted: 11/09/2006] [Indexed: 10/23/2022]
Abstract
DNA-binding proteins play pivotal roles in transcription, DNA-replication, recombination/repair and determine cell-fate in all physiological conditions of differentiation, development and disease. As they are present in extremely small amounts in cells, their isolation/identification, particularly from scarce tissues is impracticable. We cloned the cDNA pool of snake (Ptyas mucosus) oocytes (a scarce tissue) in bacteria, overexpressed total library, purified and identified DNA-binding proteins expressed in the library. Although snake databases do not exist, we identified 23 DNA-binding proteins, obtained 10-15 amino acids internal sequence tags of six of them and succeeded in PCR amplification of the cDNAs of five proteins. We employed electro spray ionization mass spectrometry, matrix assisted laser desorption/ionization time of flight and analyzed the results by peptide mass fingerprint (PMF) and various sequence BLAST analyses. Proteins identified were largely unanimous between the PMF and BLAST analyses. We expect these proteins to play important roles in snake embryonic development and differentiation. We arrived at homologous mouse proteins to some of the identified snake proteins and are working towards characterizing their structure and physiological function. Similar approaches shall prove valuable in isolation and identification of important factors from scarce carcinoma tissues, mammalian oocytes and early embryos, which might be involved in important functions like nuclear reprogramming, embryonic development and differentiation.
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MESH Headings
- Animals
- Chromatography, Affinity
- Cloning, Molecular
- Colubridae/embryology
- Colubridae/genetics
- DNA, Complementary/genetics
- DNA-Binding Proteins/chemistry
- DNA-Binding Proteins/isolation & purification
- DNA-Binding Proteins/physiology
- Databases, Protein
- Electrophoresis, Gel, Two-Dimensional
- Electrophoresis, Polyacrylamide Gel
- Embryo, Nonmammalian
- Female
- Gene Library
- Oocytes/metabolism
- Peptide Mapping
- Polymerase Chain Reaction
- Protein Binding
- Sequence Analysis, Protein
- Spectrometry, Mass, Electrospray Ionization
- Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
- Trypsin/pharmacology
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Affiliation(s)
- Mala Ganesan
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
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23
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Langlois RE, Carson MB, Bhardwaj N, Lu H. Learning to translate sequence and structure to function: identifying DNA binding and membrane binding proteins. Ann Biomed Eng 2007; 35:1043-52. [PMID: 17436108 PMCID: PMC2706547 DOI: 10.1007/s10439-007-9312-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2006] [Accepted: 04/02/2007] [Indexed: 10/23/2022]
Abstract
A protein's function depends in a large part on interactions with other molecules. With an increasing number of protein structures becoming available every year, a corresponding structural annotation approach identifying such interactions grows more expedient. At the same time, machine learning has gained popularity in bioinformatics providing robust annotation of genes and proteins without sequence homology. Here we have developed a general machine learning protocol to identify proteins that bind DNA and membrane. In general, there is no theory or even rule of thumb to pick the best machine learning algorithm. Thus, a systematic comparison of several classification algorithms known to perform well is investigated. Indeed, the boosted tree classifier is found to give the best performance, achieving 93% and 88% accuracy to discriminate non-homologous proteins that bind membrane and DNA, respectively, significantly outperforming all previously published works. We also attempted to address the importance of the attributes in function prediction and the relationships between relevant attributes. A graphical model based on boosted trees is applied to study the important features in discriminating DNA-binding proteins. In summary, the current protocol identified physical features important in DNA and membrane binding, rather than annotating function through sequence similarity.
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Affiliation(s)
| | | | | | - Hui Lu
- Corresponding Author: Hui Lu 851 S Morgan, Rm 218, M/C063 Chicago, IL 60607 Phone: (312) 413−2021 Fax: (312) 413−2018
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24
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Hellman LM, Fried MG. Electrophoretic mobility shift assay (EMSA) for detecting protein-nucleic acid interactions. Nat Protoc 2007; 2:1849-61. [PMID: 17703195 PMCID: PMC2757439 DOI: 10.1038/nprot.2007.249] [Citation(s) in RCA: 760] [Impact Index Per Article: 44.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The gel electrophoresis mobility shift assay (EMSA) is used to detect protein complexes with nucleic acids. It is the core technology underlying a wide range of qualitative and quantitative analyses for the characterization of interacting systems. In the classical assay, solutions of protein and nucleic acid are combined and the resulting mixtures are subjected to electrophoresis under native conditions through polyacrylamide or agarose gel. After electrophoresis, the distribution of species containing nucleic acid is determined, usually by autoradiography of 32P-labeled nucleic acid. In general, protein-nucleic acid complexes migrate more slowly than the corresponding free nucleic acid. In this protocol, we identify the most important factors that determine the stabilities and electrophoretic mobilities of complexes under assay conditions. A representative protocol is provided and commonly used variants are discussed. Expected outcomes are briefly described. References to extensions of the method and a troubleshooting guide are provided.
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Affiliation(s)
- Lance M. Hellman
- Department of Molecular and Cellular Biochemistry, University of Kentucky 741 S. Limestone Street, Lexington, Kentucky, 40536-0509, USA
| | - Michael G. Fried
- Department of Molecular and Cellular Biochemistry, University of Kentucky 741 S. Limestone Street, Lexington, Kentucky, 40536-0509, USA
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25
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Abstract
One of our long-term interests is to explore the immunogenic sugar moieties that are important for “self-” and “nonself” discrimination and host immune responses. We have established a highthroughput platform of carbohydrate microarrays to facilitate these investigations. Using this technology, carbohydrate-containing macromolecules of distinct structural configurations, including polysaccharides, natural glycoconjugates, and mono- and oligosaccharides coupled to lipid, polyacrylamide, and protein carriers, have been tested for microarray construction without further chemical modification. Here, we discuss issues related to the establishment of this technology and areas that are highly promising for its application. We also provide an example to illustrate that the carbohydrate microarray is a discovery tool; it is particularly useful for identifying immunological sugar moieties, including differentially expressed complex carbohydrates of cancer cells and stem cells as well as sugar signatures of previously unrecognized microbial pathogens.
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26
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Oehler S, Alberti S, Müller-Hill B. Induction of the lac promoter in the absence of DNA loops and the stoichiometry of induction. Nucleic Acids Res 2006; 34:606-12. [PMID: 16432263 PMCID: PMC1345695 DOI: 10.1093/nar/gkj453] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
In vivo induction of the Escherichia coli lactose operon as a function of inducer concentration generates a sigmoidal curve, indicating a non-linear response. Suggested explanations for this dependence include a 2:1 inducer–repressor stoichiometry of induction, which is the currently accepted view. It is, however, known for decades that, in vitro, operator binding as a function of inducer concentration is not sigmoidal. This discrepancy between in vivo and in vitro data has so far not been resolved. We demonstrate that the in vivo non-linearity of induction is due to cooperative repression of the wild-type lac operon through DNA loop formation. In the absence of DNA loops, in vivo induction curves are hyperbolic. In the light of this result, we re-address the question of functional molecular inducer–repressor stoichiometry in induction of the lac operon.
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Affiliation(s)
- Stefan Oehler
- IMBB-FoRTH, PO Box 1385, GR-71110 Heraklion, Crete, Greece.
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27
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Ramprakesh J, Schwarz FP. Energetic differences between the specific binding of a 40bp DNA duplex and the lac promoter to lac repressor protein. Arch Biochem Biophys 2005; 438:162-73. [PMID: 15916747 DOI: 10.1016/j.abb.2005.04.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2005] [Revised: 04/22/2005] [Accepted: 04/26/2005] [Indexed: 11/27/2022]
Abstract
The energetics of LRP binding to a 104 bp lac promoter determined from ITC measurements were compared to the energetics of binding to a shorter 40 bp DNA duplex with the 21 bp promoter binding site sequence. The promoter binding affinity of 2.47 +/- 0.0 1x 10(7) M(-1) was higher than the DNA binding affinity of 1.81 +/- 0.67 x 10(7) M(-1) while the binding enthalpy of -804 +/- 41 kJ mol(-1) was lower than that of the DNA binding enthalpy of -145 +/- 16 kJ mol(-1) at 298.15 K. Both the promoter and DNA binding reactions were exothermic in phosphate buffer but endothermic in Tris buffer that showed the transfer of four protons to LRP in the former reaction but only two in the latter. A more complicated dependence of these parameters on temperature was observed for promoter binding. These energetic differences are attributable to additional LRP-promoter interactions from wrapping of the promoter around the LRP.
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Affiliation(s)
- Jayanthi Ramprakesh
- Center for Advanced Research in Biotechnology/National Institute of Standards and Technology, Rockville, MD 20850, USA
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28
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Forde CE, McCutchen-Maloney SL. Characterization of transcription factors by mass spectrometry and the role of SELDI-MS. MASS SPECTROMETRY REVIEWS 2002; 21:419-439. [PMID: 12666149 DOI: 10.1002/mas.10040] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Over the last decade, much progress has been made in the field of biological mass spectrometry, with numerous advances in technology, resolution, and affinity capture. The field of genomics has also been transformed by the sequencing and characterization of entire genomes. Some of the next challenges lie in understanding the relationship between the genome and the proteome, the protein complement of the genome, and in characterizing the regulatory processes involved in progressing from gene to functional protein. In this new age of proteomics, development of mass spectrometry methods to characterize transcription factors promises to add greatly to our understanding of regulatory networks that govern expression. However, at this time, regulatory networks of transcription factors are mostly uncharted territory. In this review, we summarize the latest advances in characterization of transcription factors by mass spectrometry including affinity capture, identification of complexes of DNA-binding proteins, structural characterization, determination of protein-DNA and protein-protein interactions, assessment of modification sites and metal binding, studies of functional activity, and the latest chip technologies that use SELDI-MS that allow the rapid capture and identification of transcription factors.
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Affiliation(s)
- Cameron E Forde
- Biodefense Division, Biology and Biotechnology Research Program, Lawrence Livermore National Laboratory, California 94550, USA
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29
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Stillman BA, Tonkinson JL. Expression microarray hybridization kinetics depend on length of the immobilized DNA but are independent of immobilization substrate. Anal Biochem 2001; 295:149-57. [PMID: 11488616 DOI: 10.1006/abio.2001.5212] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Expression microarrays are often constructed by the immobilization of PCR products on two-dimensional modified glass slides or on three-dimensional microporous substrates. In this study we investigate whether the length of the immobilized species and the substrate choice influence hybridization dynamics. Using a simple bimolecular mass action controlled model to describe hybridization, we observed that the extent of hybridization and the initial velocities were directly dependent on the length of the immobilized species. An inflection point was noted at a length of 712 bases, above which the influence of length on hybridization rate decreased. Interestingly, we observed no differences in these parameters whether hybridization occurred on a two- or three-dimensional surface. Furthermore, the affinity of the solution phase labeled species for the immobilized species was identical for all arrayed lengths on both surfaces. These data indicate a similar interaction of the noncovalently immobilized species with either surface. Finally, we have determined that competitive hybridization on expression microarrays is nonlinear with respect to time and concentration of competitor. This observation is critical for analysis of expression array data.
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Affiliation(s)
- B A Stillman
- Schleicher & Schuell, Inc., 10 Optical Avenue, Keene, NH 03431, USA
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30
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Cerutti ML, Centeno JM, Goldbaum FA, de Prat-Gay G. Generation of sequence-specific, high affinity anti-DNA antibodies. J Biol Chem 2001; 276:12769-73. [PMID: 11279040 DOI: 10.1074/jbc.m100260200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
By taking advantage of the extreme stability of a protein-DNA complex, we have obtained two highly specific monoclonal antibodies against a predetermined palindromic DNA sequence corresponding to the binding site of the E2 transcriptional regulator of the human papillomavirus (HPV-16). The purified univalent antibody fragments bind to a double-stranded DNA oligonucleotide corresponding to the E2 binding site in solution with dissociation constants in the low and subnanomolar range. This affinity matches that of the natural DNA binding domain and is severalfold higher than the affinity of a homologous bovine E2 C-terminal domain (BPV-1) for the same DNA. These antibodies discriminate effectively among a number of double- and single-stranded synthetic DNAs with factors ranging from 125- to 20,000-fold the dissociation constant of the specific DNA sequence used in the immunogenic protein-DNA complex. Moreover, they are capable of fine specificity tuning, since they both bind less tightly to another HPV-16 E2 binding site, differing in only 1 base pair in a noncontact flexible region. Beyond the relevance of obtaining a specific anti-DNA response, these results provide a first glance at how DNA as an antigen is recognized specifically by an antibody. The accuracy of the spectroscopic method used for the binding analysis suggests that a detailed mechanistic analysis is attainable.
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Affiliation(s)
- M L Cerutti
- Instituto de Investigaciones Bioquimicas, Fundación Campomar and Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Patricias Argentinas 435, (1405) Buenos Aires, Argentina
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31
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Affiliation(s)
- H Gadgil
- Department of Biochemistry, University of Tennessee, 858 Madison Avenue, Memphis, Tennessee 38163, USA
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32
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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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