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Bradley NP, Wahl KL, Steenwyk JL, Rokas A, Eichman BF. Resistance-Guided Mining of Bacterial Genotoxins Defines a Family of DNA Glycosylases. mBio 2022; 13:e0329721. [PMID: 35311535 PMCID: PMC9040887 DOI: 10.1128/mbio.03297-21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Accepted: 02/22/2022] [Indexed: 11/20/2022] Open
Abstract
Unique DNA repair enzymes that provide self-resistance against therapeutically important, genotoxic natural products have been discovered in bacterial biosynthetic gene clusters (BGCs). Among these, the DNA glycosylase AlkZ is essential for azinomycin B production and belongs to the HTH_42 superfamily of uncharacterized proteins. Despite their widespread existence in antibiotic producers and pathogens, the roles of these proteins in production of other natural products are unknown. Here, we determine the evolutionary relationship and genomic distribution of all HTH_42 proteins from Streptomyces and use a resistance-based genome mining approach to identify homologs associated with known and uncharacterized BGCs. We find that AlkZ-like (AZL) proteins constitute one distinct HTH_42 subfamily and are highly enriched in BGCs and variable in sequence, suggesting each has evolved to protect against a specific secondary metabolite. As a validation of the approach, we show that the AZL protein, HedH4, associated with biosynthesis of the alkylating agent hedamycin, excises hedamycin-DNA adducts with exquisite specificity and provides resistance to the natural product in cells. We also identify a second, phylogenetically and functionally distinct subfamily whose proteins are never associated with BGCs, are highly conserved with respect to sequence and genomic neighborhood, and repair DNA lesions not associated with a particular natural product. This work delineates two related families of DNA repair enzymes-one specific for complex alkyl-DNA lesions and involved in self-resistance to antimicrobials and the other likely involved in protection against an array of genotoxins-and provides a framework for targeted discovery of new genotoxic compounds with therapeutic potential. IMPORTANCE Bacteria are rich sources of secondary metabolites that include DNA-damaging genotoxins with antitumor/antibiotic properties. Although Streptomyces produce a diverse number of therapeutic genotoxins, efforts toward targeted discovery of biosynthetic gene clusters (BGCs) producing DNA-damaging agents is lacking. Moreover, work on toxin-resistance genes has lagged behind our understanding of those involved in natural product synthesis. Here, we identified over 70 uncharacterized BGCs producing potentially novel genotoxins through resistance-based genome mining using the azinomycin B-resistance DNA glycosylase AlkZ. We validate our analysis by characterizing the enzymatic activity and cellular resistance of one AlkZ ortholog in the BGC of hedamycin, a potent DNA alkylating agent. Moreover, we uncover a second, phylogenetically distinct family of proteins related to Escherichia coli YcaQ, a DNA glycosylase capable of unhooking interstrand DNA cross-links, which differs from the AlkZ-like family in sequence, genomic location, proximity to BGCs, and substrate specificity. This work defines two families of DNA glycosylase for specialized repair of complex genotoxic natural products and generalized repair of a broad range of alkyl-DNA adducts and provides a framework for targeted discovery of new compounds with therapeutic potential.
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Affiliation(s)
- Noah P. Bradley
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee, USA
| | - Katherine L. Wahl
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee, USA
| | - Jacob L. Steenwyk
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee, USA
| | - Antonis Rokas
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee, USA
- Department of Biomedical Informatics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Brandt F. Eichman
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee, USA
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
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Chen X, Bradley NP, Lu W, Wahl KL, Zhang M, Yuan H, Hou XF, Eichman B, Tang GL. Base excision repair system targeting DNA adducts of trioxacarcin/LL-D49194 antibiotics for self-resistance. Nucleic Acids Res 2022; 50:2417-2430. [PMID: 35191495 PMCID: PMC8934636 DOI: 10.1093/nar/gkac085] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 01/10/2022] [Accepted: 01/27/2022] [Indexed: 12/25/2022] Open
Abstract
Two families of DNA glycosylases (YtkR2/AlkD, AlkZ/YcaQ) have been found to remove bulky and crosslinking DNA adducts produced by bacterial natural products. Whether DNA glycosylases eliminate other types of damage formed by structurally diverse antibiotics is unknown. Here, we identify four DNA glycosylases-TxnU2, TxnU4, LldU1 and LldU5-important for biosynthesis of the aromatic polyketide antibiotics trioxacarcin A (TXNA) and LL-D49194 (LLD), and show that the enzymes provide self-resistance to the producing strains by excising the intercalated guanine adducts of TXNA and LLD. These enzymes are highly specific for TXNA/LLD-DNA lesions and have no activity toward other, less stable alkylguanines as previously described for YtkR2/AlkD and AlkZ/YcaQ. Similarly, TXNA-DNA adducts are not excised by other alkylpurine DNA glycosylases. TxnU4 and LldU1 possess unique active site motifs that provide an explanation for their tight substrate specificity. Moreover, we show that abasic (AP) sites generated from TxnU4 excision of intercalated TXNA-DNA adducts are incised by AP endonuclease less efficiently than those formed by 7mG excision. This work characterizes a distinct class of DNA glycosylase acting on intercalated DNA adducts and furthers our understanding of specific DNA repair self-resistance activities within antibiotic producers of structurally diverse, highly functionalized DNA damaging agents.
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Affiliation(s)
- Xiaorong Chen
- School of Chemistry and Materials Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, 1 Sub-lane Xiangshan, Hangzhou 310024, China
- State Key Laboratory of Bioorganic and Natural Products Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032, China
| | - Noah P Bradley
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA
| | - Wei Lu
- State Key Laboratory of Bioorganic and Natural Products Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032, China
| | - Katherine L Wahl
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA
| | - Mei Zhang
- State Key Laboratory of Bioorganic and Natural Products Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032, China
| | - Hua Yuan
- State Key Laboratory of Bioorganic and Natural Products Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032, China
| | - Xian-Feng Hou
- State Key Laboratory of Bioorganic and Natural Products Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032, China
| | - Brandt F Eichman
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37232, USA
| | - Gong-Li Tang
- School of Chemistry and Materials Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, 1 Sub-lane Xiangshan, Hangzhou 310024, China
- State Key Laboratory of Bioorganic and Natural Products Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032, China
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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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Hendershot JM, O'Brien PJ. Transient Kinetic Methods for Mechanistic Characterization of DNA Binding and Nucleotide Flipping. Methods Enzymol 2017; 592:377-415. [PMID: 28668128 DOI: 10.1016/bs.mie.2017.04.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Enzymes that modify nucleobases in double-stranded genomic DNA, either as part of a DNA repair pathway or as an epigenetic modifying pathway, adopt a multistep pathway to locate target sites and reconfigure the DNA to gain access. Work on several different enzymes has shown that in almost all cases base flipping, also known as nucleotide flipping, is a key feature of specific site recognition. In this chapter, we discuss some of the strategies that can be used to perform a kinetic characterization for DNA binding and nucleotide flipping. The resulting kinetic and thermodynamic framework provides a platform for understanding substrate specificity, mechanisms of inhibition, and the roles of important amino acids. We use a human DNA repair glycosylase called alkyladenine DNA glycosylase as a case study, because this is one of the best-characterized nucleotide-flipping enzymes. However, the approaches that are described can be readily adapted to study other enzymes, and future studies are needed to understand the mechanism of substrate recognition in each individual case. As more enzymes are characterized, we can hope to uncover which features of DNA searching and nucleotide flipping are fundamental features shared by many different families of DNA modifying enzymes, and which features are specific to a particular enzyme. Such an understanding provides reasonable models for less characterized enzymes that are important for epigenetic DNA modification and DNA repair pathways.
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Affiliation(s)
| | - Patrick J O'Brien
- University of Michigan Medical School, Ann Arbor, MI, United States.
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Jiang SY, Ramachandran S. Expansion Mechanisms and Evolutionary History on Genes Encoding DNA Glycosylases and Their Involvement in Stress and Hormone Signaling. Genome Biol Evol 2016; 8:1165-84. [PMID: 27026054 PMCID: PMC4860697 DOI: 10.1093/gbe/evw067] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
DNA glycosylases catalyze the release of methylated bases. They play vital roles in the base excision repair pathway and might also function in DNA demethylation. At least three families of DNA glycosylases have been identified, which included 3′-methyladenine DNA glycosylase (MDG) I, MDG II, and HhH-GPD (Helix–hairpin–Helix and Glycine/Proline/aspartate (D)). However, little is known on their genome-wide identification, expansion, and evolutionary history as well as their expression profiling and biological functions. In this study, we have genome-widely identified and evolutionarily characterized these family members. Generally, a genome encodes only one MDG II gene in most of organisms. No MDG I or MDG II gene was detected in green algae. However, HhH-GPD genes were detectable in all available organisms. The ancestor species contain small size of MDG I and HhH-GPD families. These two families were mainly expanded through the whole-genome duplication and segmental duplication. They were evolutionarily conserved and were generally under purifying selection. However, we have detected recent positive selection among the Oryza genus, which might play roles in species divergence. Further investigation showed that expression divergence played important roles in gene survival after expansion. All of these family genes were expressed in most of developmental stages and tissues in rice plants. High ratios of family genes were downregulated by drought and fungus pathogen as well as abscisic acid (ABA) and jasmonic acid (JA) treatments, suggesting a negative regulation in response to drought stress and pathogen infection through ABA- and/or JA-dependent hormone signaling pathway.
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Affiliation(s)
- Shu-Ye Jiang
- Genome Structural Biology Group, Temasek Life Science Laboratory, The National University of Singapore, Singapore
| | - Srinivasan Ramachandran
- Genome Structural Biology Group, Temasek Life Science Laboratory, The National University of Singapore, Singapore
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The Inhibitory Effect of Non-Substrate and Substrate DNA on the Ligation and Self-Adenylylation Reactions Catalyzed by T4 DNA Ligase. PLoS One 2016; 11:e0150802. [PMID: 26954034 PMCID: PMC4782999 DOI: 10.1371/journal.pone.0150802] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Accepted: 02/19/2016] [Indexed: 02/02/2023] Open
Abstract
DNA ligases are essential both to in vivo replication, repair and recombination processes, and in vitro molecular biology protocols. Prior characterization of DNA ligases through gel shift assays has shown the presence of a nick site to be essential for tight binding between the enzyme and its dsDNA substrate, with no interaction evident on dsDNA lacking a nick. In the current study, we observed a significant substrate inhibition effect, as well as the inhibition of both the self-adenylylation and nick-sealing steps of T4 DNA ligase by non-nicked, non-substrate dsDNA. Inhibition by non-substrate DNA was dependent only on the total DNA concentration rather than the structure; with 1 μg/mL of 40-mers, 75-mers, or circular plasmid DNA all inhibiting ligation equally. A >15-fold reduction in T4 DNA ligase self-adenylylation rate when in the presence of high non-nicked dsDNA concentrations was observed. Finally, EMSAs were utilized to demonstrate that non-substrate dsDNA can compete with nicked dsDNA substrates for enzyme binding. Based upon these data, we hypothesize the inhibition of T4 DNA ligase by non-nicked dsDNA is direct evidence for a two-step nick-binding mechanism, with an initial, nick-independent, transient dsDNA-binding event preceding a transition to a stable binding complex in the presence of a nick site.
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