title: Structural basis for processivity and antiviral drug toxicity in human mitochondrial DNA replicase.
abstract: The human DNA polymerase gamma (Pol γ) is responsible for DNA replication in mitochondria. Pol γ is particularly susceptible to inhibition by dideoxynucleoside-based inhibitors designed to fight viral infection. Here, we report crystal structures of the replicating Pol γ-DNA complex bound to either substrate or zalcitabine, an inhibitor used for HIV reverse transcriptase. The structures reveal that zalcitabine binds to the Pol γ active site almost identically to the substrate dCTP, providing a structural basis for Pol γ-mediated drug toxicity. When compared to the apo form, Pol γ undergoes intra- and inter-subunit conformational changes upon formation of the ternary complex with primer/template DNA and substrate. We also find that the accessory subunit Pol γB, which lacks intrinsic enzymatic activity and does not contact the primer/template DNA directly, serves as an allosteric regulator of holoenzyme activities. The structures presented here suggest a mechanism for processivity of the holoenzyme and provide a model for understanding the deleterious effects of Pol γ mutations in human disease. Crystal structures of the mitochondrial DNA polymerase, Pol γ, in complex with substrate or antiviral inhibitor zalcitabine provide a basis for understanding Pol γ-mediated drug toxicity.
authors.affiliation: Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX, USA.
authors.forename: Michal R
authors.initials: MR
authors.lastname: Szymanski
authors.affiliation: Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX, USA.
authors.forename: Vladmir B
authors.initials: VB
authors.lastname: Kuznetsov
authors.affiliation: Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX, USA.
authors.forename: Christie
authors.initials: C
authors.lastname: Shumate
authors.affiliation: Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA.
authors.forename: Qingchao
authors.initials: Q
authors.lastname: Meng
authors.affiliation: Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA.
authors.forename: Young-Sam
authors.initials: YS
authors.lastname: Lee
authors.affiliation: Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ, USA.
authors.forename: Gayatri
authors.initials: G
authors.lastname: Patel
authors.affiliation: Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ, USA.
authors.forename: Smita
authors.initials: S
authors.lastname: Patel
authors.affiliation: Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, USA Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX, USA ywyin@utmb.edu.
authors.forename: Y Whitney
authors.initials: YW
authors.lastname: Yin
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D000074002:DNA Polymerase gamma; D004272:DNA, Mitochondrial / Q000378:metabolism; D004259:DNA-Directed DNA Polymerase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D018894:Reverse Transcriptase Inhibitors / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D016047:Zalcitabine / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*
chemical_list: D004272:DNA, Mitochondrial; D018894:Reverse Transcriptase Inhibitors; D016047:Zalcitabine; D000074002:DNA Polymerase gamma; D004259:DNA-Directed DNA Polymerase; C413027:POLG protein, human
keywords: DNA replication; drug toxicity; human DNA polymerase gamma; mitochondrial toxicity; nucleoside reverse transcriptase inhibitors