1
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Tsuboyama K, Dauparas J, Chen J, Laine E, Mohseni Behbahani Y, Weinstein JJ, Mangan NM, Ovchinnikov S, Rocklin GJ. Mega-scale experimental analysis of protein folding stability in biology and design. Nature 2023; 620:434-444. [PMID: 37468638 PMCID: PMC10412457 DOI: 10.1038/s41586-023-06328-6] [Citation(s) in RCA: 44] [Impact Index Per Article: 44.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2023] [Accepted: 06/14/2023] [Indexed: 07/21/2023]
Abstract
Advances in DNA sequencing and machine learning are providing insights into protein sequences and structures on an enormous scale1. However, the energetics driving folding are invisible in these structures and remain largely unknown2. The hidden thermodynamics of folding can drive disease3,4, shape protein evolution5-7 and guide protein engineering8-10, and new approaches are needed to reveal these thermodynamics for every sequence and structure. Here we present cDNA display proteolysis, a method for measuring thermodynamic folding stability for up to 900,000 protein domains in a one-week experiment. From 1.8 million measurements in total, we curated a set of around 776,000 high-quality folding stabilities covering all single amino acid variants and selected double mutants of 331 natural and 148 de novo designed protein domains 40-72 amino acids in length. Using this extensive dataset, we quantified (1) environmental factors influencing amino acid fitness, (2) thermodynamic couplings (including unexpected interactions) between protein sites, and (3) the global divergence between evolutionary amino acid usage and protein folding stability. We also examined how our approach could identify stability determinants in designed proteins and evaluate design methods. The cDNA display proteolysis method is fast, accurate and uniquely scalable, and promises to reveal the quantitative rules for how amino acid sequences encode folding stability.
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Affiliation(s)
- Kotaro Tsuboyama
- Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
- Center for Synthetic Biology, Northwestern University, Evanston, IL, USA
- PRESTO, Japan Science and Technology Agency, Tokyo, Japan
- Institute of Industrial Science, The University of Tokyo, Tokyo, Japan
| | - Justas Dauparas
- Department of Biochemistry, University of Washington, Seattle, WA, USA
- Institute for Protein Design, University of Washington, Seattle, WA, USA
| | - Jonathan Chen
- Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
- Center for Synthetic Biology, Northwestern University, Evanston, IL, USA
- McCormick School of Engineering, Northwestern University, Evanston, IL, USA
| | - Elodie Laine
- Sorbonne Université, CNRS, IBPS, Laboratory of Computational and Quantitative Biology (LCQB), UMR 7238, Paris, France
| | - Yasser Mohseni Behbahani
- Sorbonne Université, CNRS, IBPS, Laboratory of Computational and Quantitative Biology (LCQB), UMR 7238, Paris, France
| | - Jonathan J Weinstein
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Niall M Mangan
- Center for Synthetic Biology, Northwestern University, Evanston, IL, USA
- Department of Engineering Sciences and Applied Mathematics, Northwestern University, Evanston, IL, USA
| | - Sergey Ovchinnikov
- John Harvard Distinguished Science Fellowship Program, Harvard University, Cambridge, MA, USA
| | - Gabriel J Rocklin
- Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.
- Center for Synthetic Biology, Northwestern University, Evanston, IL, USA.
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2
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Greenwood SN, Kulkarni RS, Mikhail M, Weiser BP. Replication Protein A Enhances Kinetics of Uracil DNA Glycosylase on ssDNA and Across DNA Junctions: Explored with a DNA Repair Complex Produced with SpyCatcher/SpyTag Ligation. Chembiochem 2023; 24:e202200765. [PMID: 36883884 PMCID: PMC10267839 DOI: 10.1002/cbic.202200765] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 03/06/2023] [Accepted: 03/08/2023] [Indexed: 03/09/2023]
Abstract
DNA repair proteins participate in extensive protein-protein interactions that promote the formation of DNA repair complexes. To understand how complex formation affects protein function during base excision repair, we used SpyCatcher/SpyTag ligation to produce a covalent complex between human uracil DNA glycosylase (UNG2) and replication protein A (RPA). Our covalent "RPA-Spy-UNG2" complex could identify and excise uracil bases in duplex areas next to ssDNA-dsDNA junctions slightly faster than the wild-type proteins, but this was highly dependent on DNA structure, as the turnover of the RPA-Spy-UNG2 complex slowed at DNA junctions where RPA tightly engaged long ssDNA sections. Conversely, the enzymes preferred uracil sites in ssDNA where RPA strongly enhanced uracil excision by UNG2 regardless of ssDNA length. Finally, RPA was found to promote UNG2 excision of two uracil sites positioned across a ssDNA-dsDNA junction, and dissociation of UNG2 from RPA enhanced this process. Our approach of ligating together RPA and UNG2 to reveal how complex formation affects enzyme function could be applied to examine other assemblies of DNA repair proteins.
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Affiliation(s)
- Sharon N Greenwood
- Department of Molecular Biology, Rowan University School of Osteopathic Medicine, Stratford, NJ 08084, USA
| | - Rashmi S Kulkarni
- Department of Molecular Biology, Rowan University School of Osteopathic Medicine, Stratford, NJ 08084, USA
| | - Michel Mikhail
- Department of Molecular Biology, Rowan University School of Osteopathic Medicine, Stratford, NJ 08084, USA
- Department of Internal Medicine, Newark Beth Israel Medical Center, Newark, NJ 07112, USA
| | - Brian P Weiser
- Department of Molecular Biology, Rowan University School of Osteopathic Medicine, Stratford, NJ 08084, USA
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3
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Baljinnyam T, Conrad JW, Sowers ML, Chang-Gu B, Herring JL, Hackfeld LC, Zhang K, Sowers LC. Characterization of a Novel Thermostable DNA Lyase Used To Prepare DNA for Next-Generation Sequencing. Chem Res Toxicol 2023; 36:162-176. [PMID: 36647573 PMCID: PMC9945173 DOI: 10.1021/acs.chemrestox.2c00172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Recently, we constructed a hybrid thymine DNA glycosylase (hyTDG) by linking a 29-amino acid sequence from the human thymine DNA glycosylase with the catalytic domain of DNA mismatch glycosylase (MIG) from M. thermoautotrophicum, increasing the overall activity of the glycosylase. Previously, it was shown that a tyrosine to lysine (Y126K) mutation in the catalytic site of MIG could convert the glycosylase activity to a lyase activity. We made the corresponding mutation to our hyTDG to create a hyTDG-lyase (Y163K). Here, we report that the hybrid mutant has robust lyase activity, has activity over a broad temperature range, and is active under multiple buffer conditions. The hyTDG-lyase cleaves an abasic site similar to endonuclease III (Endo III). In the presence of β-mercaptoethanol (β-ME), the abasic site unsaturated aldehyde forms a β-ME adduct. The hyTDG-lyase maintains its preference for cleaving opposite G, as with the hyTDG glycosylase, and the hyTDG-lyase and hyTDG glycosylase can function in tandem to cleave T:G mismatches. The hyTDG-lyase described here should be a valuable tool in studies examining DNA damage and repair. Future studies will utilize these enzymes to quantify T:G mispairs in cells, tissues, and genomic DNA using next-generation sequencing.
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Affiliation(s)
- Tuvshintugs Baljinnyam
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas77555, United States
| | - James W Conrad
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas77555, United States
| | - Mark L Sowers
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas77555, United States.,MD-PhD Combined Degree Program University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas77555, United States
| | - Bruce Chang-Gu
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas77555, United States.,MD-PhD Combined Degree Program University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas77555, United States
| | - Jason L Herring
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas77555, United States
| | - Linda C Hackfeld
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas77555, United States
| | - Kangling Zhang
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas77555, United States
| | - Lawrence C Sowers
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas77555, United States.,Department of Internal Medicine, University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas77555, United States
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4
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Servius HW, Pidugu LS, Sherman ME, Drohat AC. Rapid excision of oxidized adenine by human thymine DNA glycosylase. J Biol Chem 2022; 299:102756. [PMID: 36460098 PMCID: PMC9800633 DOI: 10.1016/j.jbc.2022.102756] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 11/23/2022] [Accepted: 11/24/2022] [Indexed: 12/03/2022] Open
Abstract
Oxidation of DNA bases generates mutagenic and cytotoxic lesions that are implicated in cancer and other diseases. Oxidative base lesions, including 7,8-dihydro-8-oxoguanine, are typically removed through base excision repair. In addition, oxidized deoxynucleotides such as 8-oxo-dGTP are depleted by sanitizing enzymes to preclude DNA incorporation. While pathways that counter threats posed by 7,8-dihydro-8-oxoguanine are well characterized, mechanisms protecting against the major adenine oxidation product, 7,8-dihydro-8-oxoadenine (oxoA), are poorly understood. Human DNA polymerases incorporate dGTP or dCTP opposite oxoA, producing mispairs that can cause A→C or A→G mutations. oxoA also perturbs the activity of enzymes acting on DNA and causes interstrand crosslinks. To inform mechanisms for oxoA repair, we characterized oxoA excision by human thymine DNA glycosylase (TDG), an enzyme known to remove modified pyrimidines, including deaminated and oxidized forms of cytosine and 5-methylcystosine. Strikingly, TDG excises oxoA from G⋅oxoA, A⋅oxoA, or C⋅oxoA pairs much more rapidly than it acts on the established pyrimidine substrates, whereas it exhibits comparable activity for T⋅oxoA and pyrimidine substrates. The oxoA activity depends strongly on base pairing and is 370-fold higher for G⋅oxoA versus T⋅oxoA pairs. The intrinsically disordered regions of TDG contribute minimally to oxoA excision, whereas two conserved residues (N140 and N191) are catalytically essential. Escherichia coli mismatch-specific uracil DNA-glycosylase lacks significant oxoA activity, exhibiting excision rates 4 to 5 orders of magnitude below that of its ortholog, TDG. Our results reveal oxoA as an unexpectedly efficient purine substrate for TDG and underscore the large evolutionary divergence of TDG and mismatch-specific uracil DNA-glycosylase.
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5
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Jun YW, Albarran E, Wilson DL, Ding J, Kool ET. Fluorescence Imaging of Mitochondrial DNA Base Excision Repair Reveals Dynamics of Oxidative Stress Responses. Angew Chem Int Ed Engl 2022; 61:e202111829. [PMID: 34851014 PMCID: PMC8792287 DOI: 10.1002/anie.202111829] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 11/04/2021] [Indexed: 02/03/2023]
Abstract
Mitochondrial function in cells declines with aging and with neurodegeneration, due in large part to accumulated mutations in mitochondrial DNA (mtDNA) that arise from deficient DNA repair. However, measuring this repair activity is challenging. We employ a molecular approach for visualizing mitochondrial base excision repair (BER) activity in situ by use of a fluorescent probe (UBER) that reacts rapidly with AP sites resulting from BER activity. Administering the probe to cultured cells revealed signals that were localized to mitochondria, enabling selective observation of mtDNA BER intermediates. The probe showed elevated DNA repair activity under oxidative stress, and responded to suppression of glycosylase activity. Furthermore, the probe illuminated the time lag between the initiation of oxidative stress and the initial step of BER. Absence of MTH1 in cells resulted in elevated demand for BER activity upon extended oxidative stress, while the absence of OGG1 activity limited glycosylation capacity.
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Affiliation(s)
- Yong Woong Jun
- Department of Chemistry, ChEM-H Institute, and Stanford Cancer Institute, Stanford University, Stanford, California, 94305, United States
| | - Eddy Albarran
- Department of Neurosurgery, Department of Neurology and Neurological Sciences, and Wu Tsai Neuroscience institute, Stanford University School of Medicine, Stanford, California, 94305, United States
| | - David L. Wilson
- Department of Chemistry, ChEM-H Institute, and Stanford Cancer Institute, Stanford University, Stanford, California, 94305, United States
| | - Jun Ding
- Department of Neurosurgery, Department of Neurology and Neurological Sciences, and Wu Tsai Neuroscience institute, Stanford University School of Medicine, Stanford, California, 94305, United States
| | - Eric T. Kool
- Department of Chemistry, ChEM-H Institute, and Stanford Cancer Institute, Stanford University, Stanford, California, 94305, United States
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6
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Jun YW, Albarran E, Wilson DL, Ding J, Kool ET. Fluorescence Imaging of Mitochondrial DNA Base Excision Repair Reveals Dynamics of Oxidative Stress Responses. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202111829] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Yong Woong Jun
- Department of Chemistry, ChEM-H Institute, and Stanford Cancer Institute Stanford University Stanford CA 94305 USA
| | - Eddy Albarran
- Department of Neurosurgery Department of Neurology and Neurological Sciences, and Wu Tsai Neuroscience institute Stanford University School of Medicine Stanford CA 94305 USA
| | - David L. Wilson
- Department of Chemistry, ChEM-H Institute, and Stanford Cancer Institute Stanford University Stanford CA 94305 USA
| | - Jun Ding
- Department of Neurosurgery Department of Neurology and Neurological Sciences, and Wu Tsai Neuroscience institute Stanford University School of Medicine Stanford CA 94305 USA
| | - Eric T. Kool
- Department of Chemistry, ChEM-H Institute, and Stanford Cancer Institute Stanford University Stanford CA 94305 USA
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7
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Pidugu LS, Bright H, Lin WJ, Majumdar C, Van Ostrand RP, David SS, Pozharski E, Drohat AC. Structural Insights into the Mechanism of Base Excision by MBD4. J Mol Biol 2021; 433:167097. [PMID: 34107280 PMCID: PMC8286355 DOI: 10.1016/j.jmb.2021.167097] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Revised: 05/24/2021] [Accepted: 06/01/2021] [Indexed: 11/28/2022]
Abstract
DNA glycosylases remove damaged or modified nucleobases by cleaving the N-glycosyl bond and the correct nucleotide is restored through subsequent base excision repair. In addition to excising threatening lesions, DNA glycosylases contribute to epigenetic regulation by mediating DNA demethylation and perform other important functions. However, the catalytic mechanism remains poorly defined for many glycosylases, including MBD4 (methyl-CpG binding domain IV), a member of the helix-hairpin-helix (HhH) superfamily. MBD4 excises thymine from G·T mispairs, suppressing mutations caused by deamination of 5-methylcytosine, and it removes uracil and modified uracils (e.g., 5-hydroxymethyluracil) mispaired with guanine. To investigate the mechanism of MBD4 we solved high-resolution structures of enzyme-DNA complexes at three stages of catalysis. Using a non-cleavable substrate analog, 2'-deoxy-pseudouridine, we determined the first structure of an enzyme-substrate complex for wild-type MBD4, which confirms interactions that mediate lesion recognition and suggests that a catalytic Asp, highly conserved in HhH enzymes, binds the putative nucleophilic water molecule and stabilizes the transition state. Observation that mutating the Asp (to Gly) reduces activity by 2700-fold indicates an important role in catalysis, but probably not one as the nucleophile in a double-displacement reaction, as previously suggested. Consistent with direct-displacement hydrolysis, a structure of the enzyme-product complex indicates a reaction leading to inversion of configuration. A structure with DNA containing 1-azadeoxyribose models a potential oxacarbenium-ion intermediate and suggests the Asp could facilitate migration of the electrophile towards the nucleophilic water. Finally, the structures provide detailed snapshots of the HhH motif, informing how these ubiquitous metal-binding elements mediate DNA binding.
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Affiliation(s)
- Lakshmi S Pidugu
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Hilary Bright
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Wen-Jen Lin
- Department of Chemistry, University of California Davis, Davis, CA 95616, USA
| | - Chandrima Majumdar
- Department of Chemistry, University of California Davis, Davis, CA 95616, USA
| | | | - Sheila S David
- Department of Chemistry, University of California Davis, Davis, CA 95616, USA
| | - Edwin Pozharski
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA; Center for Biomolecular Therapeutics, Institute for Bioscience and Biotechnology Research, Rockville, MD 20850, USA.
| | - Alexander C Drohat
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
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8
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Ruan J, Wu M, Ye X, Zhao S, Liang J, Ye L, You Z, Zhong B. Comparative mRNA and LncRNA Analysis of the Molecular Mechanisms Associated With Low Silk Production in Bombyx mori. Front Genet 2021; 11:592128. [PMID: 33552120 PMCID: PMC7859555 DOI: 10.3389/fgene.2020.592128] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Accepted: 12/18/2020] [Indexed: 01/04/2023] Open
Abstract
Naked pupa sericin and Naked pupa are two mutant strains of Bombyx mori with extremely low or no fibroin production compared to the Qiufeng and Baiyu strains, both of which exhibit very high silk fibroin production. However, the molecular mechanisms by which long non-coding RNAs regulate fibroin synthesis need further study. In this study, we performed high-throughput RNA-seq to investigate lncRNA and mRNA expression profiles in the posterior silk gland of Qiufeng, Baiyu, Nd-sD, and Nd silkworms at the third day of the 5th instar. Our efforts yielded 26,767 novel lncRNAs and 6,009 novel mRNAs, the expression levels of silk protein genes and silk gland transcription factors were decreased in Qiufeng vs. Nd-sD and Qiufeng vs. Nd, while those of many genes related to autophagy, apoptosis, RNA degradation, ubiquitin-mediated proteolysis and heat shock proteins were increased. Moreover, the expression of a large number of genes responsible for protein synthesis and secretion was significantly decreased in Nd. GO and KEGG analysis results showed that nucleotide excision repair, mRNA surveillance pathways, amino acid degradation, protein digestion and absorption, ER-associated degradation and proteasome pathways were significantly enriched for the Qiufeng vs. Nd-sD and Qiufeng vs. Nd comparisons. In conclusion, our findings contribute to the lncRNA and mRNA database of Bombyx mori, and the identified differentially expressed mRNAs and lncRNAs help to reveal the molecular mechanisms of low silk production in Nd-sD and Nd, providing new insights for improvement of silk yield and elucidation of silk mechanical properties.
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Affiliation(s)
- Jinghua Ruan
- College of Animal Sciences, Zhejiang University, Hangzhou, China
| | - Meiyu Wu
- College of Animal Sciences, Zhejiang University, Hangzhou, China
| | - Xiaogang Ye
- College of Animal Sciences, Zhejiang University, Hangzhou, China
| | - Shuo Zhao
- College of Animal Sciences, Zhejiang University, Hangzhou, China
| | - Jianshe Liang
- College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, China
| | - Lupeng Ye
- College of Animal Sciences, Zhejiang University, Hangzhou, China
| | - Zhengying You
- College of Animal Sciences, Zhejiang University, Hangzhou, China.,College of Life Sciences and Medicine, Zhejiang Sci-Tech University, Hangzhou, China
| | - Boxiong Zhong
- College of Animal Sciences, Zhejiang University, Hangzhou, China
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9
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Baldwin MR, Admiraal SJ, O'Brien PJ. Transient kinetic analysis of oxidative dealkylation by the direct reversal DNA repair enzyme AlkB. J Biol Chem 2020; 295:7317-7326. [PMID: 32284330 PMCID: PMC7247310 DOI: 10.1074/jbc.ra120.013517] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2020] [Revised: 04/10/2020] [Indexed: 11/06/2022] Open
Abstract
AlkB is a bacterial Fe(II)- and 2-oxoglutarate-dependent dioxygenase that repairs a wide range of alkylated nucleobases in DNA and RNA as part of the adaptive response to exogenous nucleic acid-alkylating agents. Although there has been longstanding interest in the structure and specificity of Escherichia coli AlkB and its homologs, difficulties in assaying their repair activities have limited our understanding of their substrate specificities and kinetic mechanisms. Here, we used quantitative kinetic approaches to determine the transient kinetics of recognition and repair of alkylated DNA by AlkB. These experiments revealed that AlkB is a much faster alkylation repair enzyme than previously reported and that it is significantly faster than DNA repair glycosylases that recognize and excise some of the same base lesions. We observed that whereas 1,N6-ethenoadenine can be repaired by AlkB with similar efficiencies in both single- and double-stranded DNA, 1-methyladenine is preferentially repaired in single-stranded DNA. Our results lay the groundwork for future studies of AlkB and its human homologs ALKBH2 and ALKBH3.
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Affiliation(s)
- Michael R Baldwin
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109-0600
| | - Suzanne J Admiraal
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109-0600
| | - Patrick J O'Brien
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109-0600.
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10
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Pidugu LS, Dai Q, Malik SS, Pozharski E, Drohat AC. Excision of 5-Carboxylcytosine by Thymine DNA Glycosylase. J Am Chem Soc 2019; 141:18851-18861. [PMID: 31693361 DOI: 10.1021/jacs.9b10376] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
5-Methylcytosine (mC) is an epigenetic mark that is written by methyltransferases, erased through passive and active mechanisms, and impacts transcription, development, diseases including cancer, and aging. Active DNA demethylation involves TET-mediated stepwise oxidation of mC to 5-hydroxymethylcytosine, 5-formylcytosine (fC), or 5-carboxylcytosine (caC), excision of fC or caC by thymine DNA glycosylase (TDG), and subsequent base excision repair. Many elements of this essential process are poorly defined, including TDG excision of caC. To address this problem, we solved high-resolution structures of human TDG bound to DNA with cadC (5-carboxyl-2'-deoxycytidine) flipped into its active site. The structures unveil detailed enzyme-substrate interactions that mediate recognition and removal of caC, many involving water molecules. Importantly, two water molecules contact a carboxylate oxygen of caC and are poised to facilitate acid-catalyzed caC excision. Moreover, a substrate-dependent conformational change in TDG modulates the hydrogen bond interactions for one of these waters, enabling productive interaction with caC. An Asn residue (N191) that is critical for caC excision is found to contact N3 and N4 of caC, suggesting a mechanism for acid-catalyzed base excision that features an N3-protonated form of caC but would be ineffective for C, mC, or hmC. We also investigated another Asn residue (N140) that is catalytically essential and strictly conserved in the TDG-MUG enzyme family. A structure of N140A-TDG bound to cadC DNA provides the first high-resolution insight into how enzyme-substrate interactions, including water molecules, are impacted by depleting the conserved Asn, informing its role in binding and addition of the nucleophilic water molecule.
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Affiliation(s)
- Lakshmi S Pidugu
- Department of Biochemistry and Molecular Biology , University of Maryland School of Medicine , Baltimore , Maryland 21201 , United States
| | - Qing Dai
- Department of Chemistry , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Shuja S Malik
- Department of Biochemistry and Molecular Biology , University of Maryland School of Medicine , Baltimore , Maryland 21201 , United States
| | - Edwin Pozharski
- Department of Biochemistry and Molecular Biology , University of Maryland School of Medicine , Baltimore , Maryland 21201 , United States.,Center for Biomolecular Therapeutics , Institute for Bioscience and Biotechnology Research , Rockville , Maryland 20850 , United States
| | - Alexander C Drohat
- Department of Biochemistry and Molecular Biology , University of Maryland School of Medicine , Baltimore , Maryland 21201 , United States
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11
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Coey CT, Drohat AC. Defining the impact of sumoylation on substrate binding and catalysis by thymine DNA glycosylase. Nucleic Acids Res 2019; 46:5159-5170. [PMID: 29660017 PMCID: PMC6007377 DOI: 10.1093/nar/gky278] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Accepted: 04/04/2018] [Indexed: 01/22/2023] Open
Abstract
Thymine DNA glycosylase (TDG) excises thymine from mutagenic G·T mispairs generated by deamination of 5-methylcytosine (mC) and it removes two mC derivatives, 5−formylcytosine (fC) and 5−carboxylcytosine (caC), in a multistep pathway for DNA demethylation. TDG is modified by small ubiquitin-like modifier (SUMO) proteins, but the impact of sumoylation on TDG activity is poorly defined and the functions of TDG sumoylation remain unclear. We determined the effect of TDG sumoylation, by SUMO-1 or SUMO-2, on substrate binding and catalytic parameters. Single turnover experiments reveal that sumoylation dramatically impairs TDG base-excision activity, such that G·T activity is reduced by ≥45-fold and fC and caC are excised slowly, with a reaction half-life of ≥9 min (37°C). Fluorescence anisotropy studies reveal that unmodified TDG binds tightly to G·fC and G·caC substrates, with dissociation constants in the low nanomolar range. While sumoylation of TDG weakens substrate binding, the residual affinity is substantial and is comparable to that of biochemically-characterized readers of fC and caC. Our findings raise the possibility that sumoylation enables TDG to function, at least transiently, as reader of fC and caC. Notably, sumoylation could potentially facilitate TDG recruitment of other proteins, including transcription factors or epigenetic regulators, to these sites in DNA.
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Affiliation(s)
- Christopher T Coey
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
| | - Alexander C Drohat
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.,Molecular and Structural Biology Program, University of Maryland Marlene and Stewart Greenebaum Comprehensive Cancer Center, Baltimore, MD 21201, USA
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12
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Dow BJ, Malik SS, Drohat AC. Defining the Role of Nucleotide Flipping in Enzyme Specificity Using 19F NMR. J Am Chem Soc 2019; 141:4952-4962. [PMID: 30841696 DOI: 10.1021/jacs.9b00146] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A broad range of proteins employ nucleotide flipping to recognize specific sites in nucleic acids, including DNA glycosylases, which remove modified nucleobases to initiate base excision repair. Deamination, a pervasive mode of damage, typically generates lesions that are recognized by glycosylases as being foreign to DNA. However, deamination of 5-methylcytosine (mC) generates thymine, a canonical DNA base, presenting a challenge for damage recognition. Nevertheless, repair of mC deamination is important because the resulting G·T mispairs cause C → T transition mutations, and mC is abundant in all three domains of life. Countering this threat are three types of glycosylases that excise thymine from G·T mispairs, including thymine DNA glycosylase (TDG). These enzymes must minimize excision of thymine that is not generated by mC deamination, in A·T pairs and in polymerase-generated G·T mispairs. TDG preferentially removes thymine from DNA contexts in which cytosine methylation is prevalent, including CG and one non-CG site. This remarkable context specificity could be attained through modulation of nucleotide flipping, a reversible step that precedes base excision. We tested this idea using fluorine NMR and DNA containing 2'-fluoro-substituted nucleotides. We find that dT nucleotide flipping depends on DNA context and is efficient only in contexts known to feature cytosine methylation. We also show that a conserved Ala residue limits thymine excision by hindering nucleotide flipping. A linear free energy correlation reveals that TDG attains context specificity for thymine excision through modulation of nucleotide flipping. Our results provide a framework for characterizing nucleotide flipping in nucleic acids using 19F NMR.
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Affiliation(s)
- Blaine J Dow
- Department of Biochemistry and Molecular Biology , University of Maryland School of Medicine , Baltimore , Maryland 21201 , United States
| | - Shuja S Malik
- Department of Biochemistry and Molecular Biology , University of Maryland School of Medicine , Baltimore , Maryland 21201 , United States
| | - Alexander C Drohat
- Department of Biochemistry and Molecular Biology , University of Maryland School of Medicine , Baltimore , Maryland 21201 , United States
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Zhang L, Reyes A, Wang X. The Role of DNA Repair in Maintaining Mitochondrial DNA Stability. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1038:85-105. [PMID: 29178071 DOI: 10.1007/978-981-10-6674-0_7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Mitochondria are vital double-membrane organelles that act as a "powerhouse" inside the cell and have essential roles to maintain cellular functions, e.g., ATP production, iron-sulfur synthesis metabolism, and steroid synthesis. An important difference with other organelles is that they contain their own mitochondrial DNA (mtDNA). Such powerful organelles are also sensitive to both endogenous and exogenous factors that can cause lesions to their structural components and their mtDNA, resulting in gene mutations and eventually leading to diseases. In this review, we will mainly focus on mammalian mitochondrial DNA repair pathways that safeguard mitochondrial DNA integrity and several important factors involved in the repair process, especially on an essential pathway, base excision repair. We eagerly anticipate to explore more methods to treat related diseases by constantly groping for these complexes and precise repair mechanisms.
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Affiliation(s)
- Linlin Zhang
- Zhongshan Hospital Institute of Clinical Science, Fudan University, Shanghai Medical College, Shanghai, China.
| | - Aurelio Reyes
- MRC Mitochondrial Biology Unit, University of Cambridge, Cambridge, UK.
| | - Xiangdong Wang
- Zhongshan Hospital Institute of Clinical Science, Fudan University, Shanghai Medical College, Shanghai, China.
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