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Westwood MN, Pilarski A, Johnson C, Mamoud S, Meints GA. Backbone Conformational Equilibrium in Mismatched DNA Correlates with Enzyme Activity. Biochemistry 2023; 62:2816-2827. [PMID: 37699121 PMCID: PMC10552547 DOI: 10.1021/acs.biochem.3c00230] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2023] [Revised: 08/25/2023] [Indexed: 09/14/2023]
Abstract
T:G mismatches in mammals arise primarily from the deamination of methylated CpG sites or the incorporation of improper nucleotides. The process by which repair enzymes such as thymine DNA glycosylase (TDG) identify a canonical DNA base in the incorrect pairing context remains a mystery. However, the abundant contacts of the repair enzymes with the DNA backbone suggest a role for protein-phosphate interaction in the recognition and repair processes, where conformational properties may facilitate the proper interactions. We have previously used 31P NMR to investigate the energetics of DNA backbone BI-BII interconversion and the effect of a mismatch or lesion compared to canonical DNA and found stepwise differences in ΔG of 1-2 kcal/mol greater than equivalent steps in unmodified DNA. We have currently compared our results to substrate dependence for TDG, MBD4, M. HhaI, and CEBPβ, testing for correlations to sequence and base-pair dependence. We found strong correlations of our DNA phosphate backbone equilibrium (Keq) to different enzyme kinetics or binding parameters of these varied enzymes, suggesting that the backbone equilibrium may play an important role in mismatch recognition and/or conformational rearrangement and energetics during nucleotide flipping or other aspects of enzyme interrogation of the DNA substrate.
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Affiliation(s)
- M. N. Westwood
- Biophysics
Program, University of Michigan, 930 N. University Avenue, Ann Arbor, Michigan 48109, United States
| | - A. Pilarski
- Department
of Chemistry and Biochemistry, Missouri
State University, 901 S. National Ave., Springfield, Missouri 65897, United States
| | - C. Johnson
- Department
of Chemistry and Biochemistry, Missouri
State University, 901 S. National Ave., Springfield, Missouri 65897, United States
| | - S. Mamoud
- Department
of Chemistry and Biochemistry, Missouri
State University, 901 S. National Ave., Springfield, Missouri 65897, United States
| | - G. A. Meints
- Department
of Chemistry and Biochemistry, Missouri
State University, 901 S. National Ave., Springfield, Missouri 65897, United States
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Kotandeniya D, Rogers MS, Fernandez J, Kanugula S, Hudson RHE, Rodriguez F, Lipscomb JD, Tretyakova N. 6-phenylpyrrolocytosine as a fluorescent probe to examine nucleotide flipping catalyzed by a DNA repair protein. Biopolymers 2020; 112:e23405. [PMID: 33098572 DOI: 10.1002/bip.23405] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 09/30/2020] [Accepted: 09/30/2020] [Indexed: 11/05/2022]
Abstract
Cellular exposure to tobacco-specific nitrosamines causes formation of promutagenic O6 -[4-oxo-4-(3-pyridyl)but-1-yl]guanine (O6 -POB-G) and O6 -methylguanine (O6 -Me-G) adducts in DNA. These adducts can be directly repaired by O6 -alkylguanine-DNA alkyltransferase (AGT). Repair begins by flipping the damaged base out of the DNA helix. AGT binding and base-flipping have been previously studied using pyrrolocytosine as a fluorescent probe paired to the O6 -alkylguanine lesion, but low fluorescence yield limited the resolution of steps in the repair process. Here, we utilize the highly fluorescent 6-phenylpyrrolo-2'-deoxycytidine (6-phenylpyrrolo-C) to investigate AGT-DNA interactions. Synthetic oligodeoxynucleotide duplexes containing O6 -POB-G and O6 -Me-G adducts were placed within the CpG sites of codons 158, 245, and 248 of the p53 tumor suppressor gene and base-paired to 6-phenylpyrrolo-C in the opposite strand. Neighboring cytosine was either unmethylated or methylated. Stopped-flow fluorescence measurements were performed by mixing the DNA duplexes with C145A or R128G AGT variants. We observe a rapid, two-step, nearly irreversible binding of AGT to DNA followed by two slower steps, one of which is base-flipping. Placing 5-methylcytosine immediately 5' to the alkylated guanosine causes a reduction in rate constant of nucleotide flipping. O6 -POB-G at codon 158 decreased the base flipping rate constant by 3.5-fold compared with O6 -Me-G at the same position. A similar effect was not observed at other codons.
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Affiliation(s)
- Delshanee Kotandeniya
- Department of Medicinal Chemistry and the Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota, USA
| | - Melanie S Rogers
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota, USA
| | - Jenna Fernandez
- Department of Medicinal Chemistry and the Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota, USA
| | - Sreenivas Kanugula
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
| | - Robert H E Hudson
- Department of Chemistry, University of Western Ontario, London, Ontario, Canada
| | - Freddys Rodriguez
- Department of Medicinal Chemistry and the Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota, USA
| | - John D Lipscomb
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota, USA
| | - Natalia Tretyakova
- Department of Medicinal Chemistry and the Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota, USA
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Zsidó BZ, Hetényi C. Molecular Structure, Binding Affinity, and Biological Activity in the Epigenome. Int J Mol Sci 2020; 21:ijms21114134. [PMID: 32531926 PMCID: PMC7311975 DOI: 10.3390/ijms21114134] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 06/07/2020] [Accepted: 06/08/2020] [Indexed: 02/07/2023] Open
Abstract
Development of valid structure–activity relationships (SARs) is a key to the elucidation of pathomechanisms of epigenetic diseases and the development of efficient, new drugs. The present review is based on selected methodologies and applications supplying molecular structure, binding affinity and biological activity data for the development of new SARs. An emphasis is placed on emerging trends and permanent challenges of new discoveries of SARs in the context of proteins as epigenetic drug targets. The review gives a brief overview and classification of the molecular background of epigenetic changes, and surveys both experimental and theoretical approaches in the field. Besides the results of sophisticated, cutting edge techniques such as cryo-electron microscopy, protein crystallography, and isothermal titration calorimetry, examples of frequently used assays and fast screening techniques are also selected. The review features how different experimental methods and theoretical approaches complement each other and result in valid SARs of the epigenome.
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Taylor EL, Kesavan PM, Wolfe AE, O'Brien PJ. Distinguishing Specific and Nonspecific Complexes of Alkyladenine DNA Glycosylase. Biochemistry 2018; 57:4440-4454. [PMID: 29940097 DOI: 10.1021/acs.biochem.8b00531] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Human alkyladenine DNA glycosylase (AAG) recognizes many alkylated and deaminated purine lesions and excises them to initiate the base excision DNA repair pathway. AAG employs facilitated diffusion to rapidly scan nonspecific sites and locate rare sites of damage. Nonspecific DNA binding interactions are critical to the efficiency of this search for damage, but little is known about the binding footprint or the affinity of AAG for nonspecific sites. We used biochemical and biophysical approaches to characterize the binding of AAG to both undamaged and damaged DNA. Although fluorescence anisotropy is routinely used to study DNA binding, we found unexpected complexities in the data for binding of AAG to DNA. Systematic comparison of different fluorescent labels and different lengths of DNA allowed binding models to be distinguished and demonstrated that AAG can bind with high affinity and high density to nonspecific DNA. Fluorescein-labeled DNA gave the most complex behavior but also showed the greatest potential to distinguish specific and nonspecific binding modes. We suggest a unified model that is expected to apply to many DNA binding proteins that exhibit affinity for nonspecific DNA. Although AAG strongly prefers to excise lesions from duplex DNA, nonspecific binding is comparable for single- and double-stranded nonspecific sites. The electrostatically driven binding of AAG to small DNA sites (∼5 nucleotides of single-stranded and ∼6 base pairs of duplex) facilitates the search for DNA damage in chromosomal DNA, which is bound by nucleosomes and other proteins.
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Affiliation(s)
- Erin L Taylor
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Preethi M Kesavan
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Abigail E Wolfe
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Patrick J O'Brien
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109 , United States
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