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Chatterjee T, Tiwari A, Gupta R, Shukla H, Varshney A, Mishra S, Habib S. A Plasmodium apicoplast-targeted unique exonuclease/FEN exhibits interspecies functional differences attributable to an insertion that alters DNA-binding. Nucleic Acids Res 2024:gkae512. [PMID: 38888125 DOI: 10.1093/nar/gkae512] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 05/30/2024] [Accepted: 06/03/2024] [Indexed: 06/20/2024] Open
Abstract
The human malaria parasite Plasmodium falciparum genome is among the most A + T rich, with low complexity regions (LCRs) inserted in coding sequences including those for proteins targeted to its essential relict plastid (apicoplast). Replication of the apicoplast genome (plDNA), mediated by the atypical multifunctional DNA polymerase PfPrex, would require additional enzymatic functions for lagging strand processing. We identified an apicoplast-targeted, [4Fe-4S]-containing, FEN/Exo (PfExo) with a long LCR insertion and detected its interaction with PfPrex. Distinct from other known exonucleases across organisms, PfExo recognized a wide substrate range; it hydrolyzed 5'-flaps, processed dsDNA as a 5'-3' exonuclease, and was a bipolar nuclease on ssDNA and RNA-DNA hybrids. Comparison with the rodent P. berghei ortholog PbExo, which lacked the insertion and [4Fe-4S], revealed interspecies functional differences. The insertion-deleted PfExoΔins behaved like PbExo with a limited substrate repertoire because of compromised DNA binding. Introduction of the PfExo insertion into PbExo led to gain of activities that the latter initially lacked. Knockout of PbExo indicated essentiality of the enzyme for survival. Our results demonstrate the presence of a novel apicoplast exonuclease with a functional LCR that diversifies substrate recognition, and identify it as the candidate flap-endonuclease and RNaseH required for plDNA replication and maintenance.
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Affiliation(s)
- Tribeni Chatterjee
- Division of Biochemistry and Structural Biology, CSIR-Central Drug Research Institute, Lucknow, India
| | - Anupama Tiwari
- Division of Biochemistry and Structural Biology, CSIR-Central Drug Research Institute, Lucknow, India
| | - Ritika Gupta
- Division of Biochemistry and Structural Biology, CSIR-Central Drug Research Institute, Lucknow, India
| | - Himadri Shukla
- Division of Molecular Microbiology and Immunology, CSIR-Central Drug Research Institute, Lucknow, India
| | - Aastha Varshney
- Division of Molecular Microbiology and Immunology, CSIR-Central Drug Research Institute, Lucknow, India
| | - Satish Mishra
- Division of Molecular Microbiology and Immunology, CSIR-Central Drug Research Institute, Lucknow, India
| | - Saman Habib
- Division of Biochemistry and Structural Biology, CSIR-Central Drug Research Institute, Lucknow, India
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2
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Clement PC, Sapam T, Nair DT. A conserved polar residue plays a critical role in mismatch detection in A-family DNA polymerases. Int J Biol Macromol 2024; 269:131965. [PMID: 38697428 DOI: 10.1016/j.ijbiomac.2024.131965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2024] [Revised: 04/26/2024] [Accepted: 04/27/2024] [Indexed: 05/05/2024]
Abstract
In A-family DNA polymerases (dPols), a functional 3'-5' exonuclease activity is known to proofread newly synthesized DNA. The identification of a mismatch in substrate DNA leads to transfer of the primer strand from the polymerase active site to the exonuclease active site. To shed more light regarding the mechanism responsible for the detection of mismatches, we have utilized DNA polymerase 1 from Aquifex pyrophilus (ApPol1). The enzyme synthesized DNA with high fidelity and exhibited maximal exonuclease activity with DNA substrates bearing mismatches at the -2 and - 3 positions. The crystal structure of apo-ApPol1 was utilized to generate a computational model of the functional ternary complex of this enzyme. The analysis of the model showed that N332 forms interactions with minor groove atoms of the base pairs at the -2 and - 3 positions. The majority of known A-family dPols show the presence of Asn at a position equivalent to N332. The N332L mutation led to a decrease in the exonuclease activity for representative purine-pyrimidine, and pyrimidine-pyrimidine mismatches at -2 and - 3 positions, respectively. Overall, our findings suggest that conserved polar residues located towards the minor groove may facilitate the detection of position-specific mismatches to enhance the fidelity of DNA synthesis.
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Affiliation(s)
- Patterson C Clement
- Regional Centre for Biotechnology, NCR Biotech Science Cluster, 3rd Milestone, Faridabad-Gurgaon Expressway, Faridabad 121 001, Haryana (NCR Delhi), India
| | - Tuleshwori Sapam
- Regional Centre for Biotechnology, NCR Biotech Science Cluster, 3rd Milestone, Faridabad-Gurgaon Expressway, Faridabad 121 001, Haryana (NCR Delhi), India
| | - Deepak T Nair
- Regional Centre for Biotechnology, NCR Biotech Science Cluster, 3rd Milestone, Faridabad-Gurgaon Expressway, Faridabad 121 001, Haryana (NCR Delhi), India.
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3
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Zhou ZX, Follonier C, Lujan SA, Burkholder AB, Zakian VA, Kunkel TA. Pif1 family helicases promote mutation avoidance during DNA replication. Nucleic Acids Res 2022; 50:12844-12855. [PMID: 36533450 PMCID: PMC9825187 DOI: 10.1093/nar/gkac1127] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2021] [Revised: 10/25/2022] [Accepted: 11/12/2022] [Indexed: 12/23/2022] Open
Abstract
Pif1 family 5' → 3' DNA helicases are important for replication fork progression and genome stability. The budding yeast Saccharomyces cerevisiae encodes two Pif1 family helicases, Rrm3 and Pif1, both of which are multi-functional. Here we describe novel functions for Rrm3 in promoting mutation avoidance during DNA replication. We show that loss of RRM3 results in elevated spontaneous mutations made by DNA polymerases Pols ϵ and δ, which are subject to DNA mismatch repair. The absence of RRM3 also causes higher mutagenesis by the fourth B-family DNA polymerase Pol ζ. By genome-wide analysis, we show that the mutational consequences due to loss of RRM3 vary depending on the genomic locus. Rrm3 promotes the accuracy of DNA replication by Pols ϵ and δ across the genome, and it is particularly important for preventing Pol ζ-dependent mutagenesis at tRNA genes. In addition, mutation avoidance by Rrm3 depends on its helicase activity, and Pif1 serves as a backup for Rrm3 in suppressing mutagenesis. We present evidence that the sole human Pif1 family helicase in human cells likely also promotes replication fidelity, suggesting that a role for Pif1 family helicases in mutation avoidance may be evolutionarily conserved, a possible underlying mechanism for its potential tumor-suppressor function.
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Affiliation(s)
- Zhi-Xiong Zhou
- Genome Integrity & Structural Biology Laboratory, Princeton University, Princeton, NJ 08544, USA
| | - Cindy Follonier
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Princeton, NJ 08544, USA
| | - Scott A Lujan
- Genome Integrity & Structural Biology Laboratory, Princeton University, Princeton, NJ 08544, USA
| | - Adam B Burkholder
- Integrative Bioinformatics Support Group, NIH/NIEHS, DHHS, Research Triangle Park, NC 27709, USA
| | - Virginia A Zakian
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Princeton, NJ 08544, USA
| | - Thomas A Kunkel
- Genome Integrity & Structural Biology Laboratory, Princeton University, Princeton, NJ 08544, USA
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4
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Nieto NS, Parrott EE, Nelson SW. Ribonucleotide Misincorporation and Reverse Transcriptase Activities of Plasmodium falciparum Apicoplast DNA Polymerase. Biochemistry 2022; 61:2742-2750. [DOI: 10.1021/acs.biochem.2c00450] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Nicholas S. Nieto
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa50011, United States
| | - Eric E. Parrott
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa50011, United States
| | - Scott W. Nelson
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa50011, United States
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5
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Kumari A, Yadav A, Lahiri I. Transient State Kinetics of Plasmodium falciparum Apicoplast DNA Polymerase Suggests the Involvement of Accessory Factors for Efficient and Accurate DNA Synthesis. Biochemistry 2022; 61:2319-2333. [PMID: 36251801 DOI: 10.1021/acs.biochem.2c00446] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Plasmodium, the causative agent of malaria, belongs to the phylum Apicomplexa. Most apicomplexans, including Plasmodium, contain an essential nonphotosynthetic plastid called the apicoplast that harbors its own genome that is replicated by a dedicated organellar replisome. This replisome employs a single DNA polymerase (apPol), which is expected to perform both replicative and translesion synthesis. Unlike other replicative polymerases, no processivity factor for apPol has been identified. While preliminary structural and biochemical studies have provided an overall characterization of apPol, the kinetic mechanism of apPol's activity remains unknown. We have used transient state methods to determine the kinetics of replicative and translesion synthesis by apPol and show that apPol has low processivity and efficiency while copying undamaged DNA. Moreover, while apPol can bypass oxidatively damaged lesions, the bypass is error-prone. Taken together, our results raise the following question─how does a polymerase with low processivity, efficiency, and fidelity (for translesion synthesis) faithfully replicate the apicoplast organellar DNA within the hostile environment of the human host? We hypothesize that interactions with putative components of the apicoplast replisome and/or an as-yet-undiscovered processivity factor transform apPol into an efficient and accurate enzyme.
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Affiliation(s)
- Anamika Kumari
- Department of Biological Sciences, Indian Institute of Science Education and Research Mohali, Punjab 140306, India
| | - Anjali Yadav
- Department of Biological Sciences, Indian Institute of Science Education and Research Mohali, Punjab 140306, India
| | - Indrajit Lahiri
- Department of Biological Sciences, Indian Institute of Science Education and Research Mohali, Punjab 140306, India.,Molecular Microbiology, School of Biosciences, University of Sheffield, Sheffield S10 2TN, U.K
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6
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Sharma M, Nair DT. Pfprex from
Plasmodium falciparum
can bypass oxidative stress‐induced DNA lesions. FEBS J 2022; 289:5218-5240. [DOI: 10.1111/febs.16414] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Revised: 01/13/2022] [Accepted: 02/25/2022] [Indexed: 12/24/2022]
Affiliation(s)
- Minakshi Sharma
- Regional Centre for Biotechnology Faridabad India
- Kalinga Institute of Industrial Technology Bhubaneshwar India
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7
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Kaur S, Nieto NS, McDonald P, Beck JR, Honzatko RB, Roy A, Nelson SW. Discovery of small molecule inhibitors of Plasmodium falciparum apicoplast DNA polymerase. J Enzyme Inhib Med Chem 2022; 37:1320-1326. [PMID: 35514163 PMCID: PMC9090415 DOI: 10.1080/14756366.2022.2070909] [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] [Indexed: 11/01/2022] Open
Abstract
Malaria is caused by infection with protozoan parasites of the Plasmodium genus, which is part of the phylum Apicomplexa. Most organisms in this phylum contain a relic plastid called the apicoplast. The apicoplast genome is replicated by a single DNA polymerase (apPOL), which is an attractive target for anti-malarial drugs. We screened small-molecule libraries (206,504 compounds) using a fluorescence-based high-throughput DNA polymerase assay. Dose/response analysis and counter-screening identified 186 specific apPOL inhibitors. Toxicity screening against human HepaRG human cells removed 84 compounds and the remaining were subjected to parasite killing assays using chloroquine resistant P. falciparum parasites. Nine compounds were potent inhibitors of parasite growth and may serve as lead compounds in efforts to discover novel malaria drugs.
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Affiliation(s)
- Supreet Kaur
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, USA
| | - Nicholas S Nieto
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, USA
| | - Peter McDonald
- High Throughput Screening Laboratory, University of Kansas, Lawrence, KS, USA
| | - Josh R Beck
- Department of Biomedical Sciences, Iowa State University, Ames, IA, USA
| | - Richard B Honzatko
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, USA
| | - Anuradha Roy
- High Throughput Screening Laboratory, University of Kansas, Lawrence, KS, USA
| | - Scott W Nelson
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, USA
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8
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Li QS, Shu YG, Ou-Yang ZC, Li M. Kinetic assays of DNA polymerase fidelity: A theoretical perspective beyond Michaelis-Menten kinetics. Phys Rev E 2021; 104:014408. [PMID: 34412358 DOI: 10.1103/physreve.104.014408] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2020] [Accepted: 06/23/2021] [Indexed: 11/07/2022]
Abstract
The high fidelity of DNA polymerase (DNAP) is critical for the faithful replication of DNA. There are several quantitative approaches to measure DNAP fidelity. Directly counting the error frequency in the replication products gives the true fidelity but it turns out very hard to implement in practice. Two biochemical kinetic approaches, the steady-state assay and the transient-state assay, were then suggested and widely adopted. In these assays, the error frequency is indirectly estimated by using kinetic theories combined with the measured apparent kinetic rates. However, whether it is equivalent to the true fidelity has never been clarified theoretically, and in particular there are different strategies using these assays to quantify the proofreading efficiency of DNAP but often lead to inconsistent results. In this paper, we make a comprehensive examination on the theoretical foundation of the two kinetic assays, based on the theory of DNAP fidelity recently proposed by us. Our studies show that while the conventional kinetic assays are generally valid to quantify the discrimination efficiency of DNAP, they are valid to quantify the proofreading efficiency of DNAP only when the kinetic parameters satisfy some constraints which will be given explicitly in this paper. These results may inspire more carefully-designed experiments to quantify DNAP fidelity.
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Affiliation(s)
- Qiu-Shi Li
- School of Physical Science, University of Chinese Academy of Sciences, No. 19(A) Yuquan Road, Shijingshan District, Beijing 101400, People's Republic of China
| | - Yao-Gen Shu
- Wenzhou Institute, University of Chinese Academy of Sciences, No 1, Jinlian Road, Longwan District, Wenzhou, Zhejiang 325000, People's Republic of China
| | - Zhong-Can Ou-Yang
- Institute of Theoretical Physics, Chinese Academy of Sciences, Zhong Guan Cun East Street 55, P. O. Box 2735, Beijing 100190, People's Republic of China
| | - Ming Li
- School of Physical Science, University of Chinese Academy of Sciences, No. 19(A) Yuquan Road, Shijingshan District, Beijing 101400, People's Republic of China
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9
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The proofreading activity of Pfprex from Plasmodium falciparum can prevent mutagenesis of the apicoplast genome by oxidized nucleotides. Sci Rep 2020; 10:11157. [PMID: 32636411 PMCID: PMC7341739 DOI: 10.1038/s41598-020-67853-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Accepted: 06/11/2020] [Indexed: 01/28/2023] Open
Abstract
The DNA polymerase module of the Pfprex enzyme (PfpPol) is responsible for duplication of the genome of the apicoplast organelle in the malaria parasite. We show that PfpPol can misincorporate oxidized nucleotides such as 8oxodGTP opposite dA. This event gives rise to transversion mutations that are known to lead to adverse physiological outcomes. The apicoplast genome is particularly vulnerable to the harmful effects of 8oxodGTP due to very high AT content (~ 87%). We show that the proofreading activity of PfpPol has the unique ability to remove the oxidized nucleotide from the primer terminus. Due to this property, the proofreading domain of PfpPol is able to prevent mutagenesis of the AT-rich apicoplast genome and neutralize the deleterious genotoxic effects of ROS generated in the apicoplast due to normal metabolic processes. The proofreading activity of the Pfprex enzyme may, therefore, represent an attractive target for therapeutic intervention. Also, a survey of DNA repair pathways shows that the observed property of Pfprex constitutes a novel form of dynamic error correction wherein the repair of promutagenic damaged nucleotides is concomitant with DNA replication.
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10
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Milton ME, Choe JY, Honzatko RB, Nelson SW. Crystal Structure of the Apicoplast DNA Polymerase from Plasmodium falciparum: The First Look at a Plastidic A-Family DNA Polymerase. J Mol Biol 2016; 428:3920-3934. [PMID: 27487482 DOI: 10.1016/j.jmb.2016.07.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Revised: 07/19/2016] [Accepted: 07/22/2016] [Indexed: 11/18/2022]
Abstract
Plasmodium falciparum, the primary cause of malaria, contains a non-photosynthetic plastid called the apicoplast. The apicoplast exists in most members of the phylum Apicomplexa and has its own genome along with organelle-specific enzymes for its replication. The only DNA polymerase found in the apicoplast (apPOL) was putatively acquired through horizontal gene transfer from a bacteriophage and is classified as an atypical A-family polymerase. Here, we present its crystal structure at a resolution of 2.9Å. P. falciparum apPOL, the first structural representative of a plastidic A-family polymerase, diverges from typical A-family members in two of three previously identified signature motifs and in a region not implicated by sequence. Moreover, apPOL has an additional N-terminal subdomain, the absence of which severely diminishes its 3' to 5' exonuclease activity. A compound known to be toxic to Plasmodium is a potent inhibitor of apPOL, suggesting that apPOL is a viable drug target. The structure provides new insights into the structural diversity of A-family polymerases and may facilitate structurally guided antimalarial drug design.
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Affiliation(s)
- Morgan E Milton
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA
| | - Jun-Yong Choe
- Department of Biochemistry and Molecular Biology, Rosalind Franklin University of Medicine and Science, North Chicago, IL 60064, USA
| | - Richard B Honzatko
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA.
| | - Scott W Nelson
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA.
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11
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Milton ME, Nelson SW. Replication and maintenance of the Plasmodium falciparum apicoplast genome. Mol Biochem Parasitol 2016; 208:56-64. [PMID: 27338018 DOI: 10.1016/j.molbiopara.2016.06.006] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Revised: 06/14/2016] [Accepted: 06/19/2016] [Indexed: 12/18/2022]
Abstract
Members of the phylum Apicomplexa are responsible for many devastating diseases including malaria (Plasmodium spp.), toxoplasmosis (Toxoplasma gondii), babesiosis (Babesia bovis), and cyclosporiasis (Cyclospora cayetanensis). Most Apicomplexans contain a unique and essential organelle called the apicoplast. Derived from an ancient chloroplast, the apicoplast replicates and maintains a 35 kilobase (kb) circular genome. Due to its essential nature within the parasite, drugs targeted to proteins involved in DNA replication and repair of the apicoplast should be potent and specific. This review summarizes the current knowledge surrounding the replication and repair of the Plasmodium falciparum apicoplast genome and identifies several putative proteins involved in replication and repair pathways.
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Affiliation(s)
- Morgan E Milton
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames IA 50011, USA
| | - Scott W Nelson
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames IA 50011, USA.
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12
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Milton ME, Choe JY, Honzatko RB, Nelson SW. Crystallization and preliminary X-ray analysis of the Plasmodium falciparum apicoplast DNA polymerase. Acta Crystallogr F Struct Biol Commun 2015; 71:333-7. [PMID: 25760711 PMCID: PMC4356312 DOI: 10.1107/s2053230x15002423] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Accepted: 02/04/2015] [Indexed: 11/11/2022] Open
Abstract
Infection by the parasite Plasmodium falciparum is the leading cause of malaria in humans. The parasite has a unique and essential plastid-like organelle called the apicoplast. The apicoplast contains a genome that undergoes replication and repair through the action of a replicative polymerase (apPOL). apPOL has no direct orthologs in mammalian polymerases and is therefore an attractive antimalarial drug target. No structural information exists for apPOL, and the Klenow fragment of Escherichia coli DNA polymerase I, which is its closest structural homolog, shares only 28% sequence identity. Here, conditions for the crystallization of and preliminary X-ray diffraction data from crystals of P. falciparum apPOL are reported. Data complete to 3.5 Å resolution were collected from a single crystal (2 × 2 × 5 µm) using a 5 µm beam. The space group P6522 (unit-cell parameters a = b = 141.8, c = 149.7 Å, α = β = 90, γ = 120°) was confirmed by molecular replacement. Refinement is in progress.
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Affiliation(s)
- Morgan E. Milton
- Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, IA 50011, USA
| | - Jun-yong Choe
- Department of Biochemistry and Molecular Biology, Rosalind Franklin University of Medicine and Science, IL 60064, USA
| | - Richard B. Honzatko
- Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, IA 50011, USA
| | - Scott W. Nelson
- Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, IA 50011, USA
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13
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Miller ME, Parrott EE, Singh R, Nelson SW. A High-Throughput Assay to Identify Inhibitors of the Apicoplast DNA Polymerase from Plasmodium falciparum. ACTA ACUST UNITED AC 2014; 19:966-72. [DOI: 10.1177/1087057114528738] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2013] [Accepted: 02/27/2014] [Indexed: 11/16/2022]
Abstract
Infection by Plasmodium falciparum is the leading cause of malaria in humans. The parasite contains a unique and essential plastid-like organelle called the apicoplast that, similar to the mitochondria and chloroplast, houses its own genome that must undergo replication and repair. The putative apicoplast replicative DNA polymerase, POM1, has no direct orthologs in mammals, making the P. falciparum POM1 an attractive antimalarial drug target. Here, we report on a fluorescent high-throughput DNA polymerase assay that relies on the ability of POM1 to perform strand-displacement synthesis through the stem of a DNA hairpin substrate, thereby separating a Cy3 dye from a quencher. Assay-validation experiments were performed using 384-well plates and resulted in a signal window of 7.90 and a Z’ factor of 0.71. A pilot screen of a 2880-compound library identified 62 possible inhibitors that cause more than 50% inhibition of polymerase activity. The simplicity and statistical robustness of the assay suggest it is well suited for the screening of novel apicoplast polymerase inhibitors that may serve as lead compounds in antimalarial drug-discovery efforts.
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Affiliation(s)
- Morgan E. Miller
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, USA
| | - Eric E. Parrott
- Biochemistry B.S./M.S. Program at Iowa State University, Ames, IA, USA
| | - Risham Singh
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, USA
- Ames Senior High School, Ames, IA, USA
| | - Scott W. Nelson
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, USA
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