title: Role of histidine 932 of the human mitochondrial DNA polymerase in nucleotide discrimination and inherited disease.
abstract: The human mitochondrial DNA polymerase (pol γ) is nuclearly encoded and is solely responsible for the replication and repair of the mitochondrial genome. The progressive accumulation of mutations within the mitochondrial genome is thought to be related to aging, and mutations in the pol γ gene are responsible for numerous heritable disorders including progressive external opthalmoplegia, Alpers syndrome, and parkinsonism. Here we investigate the kinetic effect of H932Y, a mutation associated with opthalmoplegia. Mutations H932Y and H932A reduce the specificity constant governing correct nucleotide incorporation 150- and 70-fold, respectively, without significantly affecting fidelity of incorporation or the maximum rate of incorporation. However, this leads to only a 2-fold reduction in rate of incorporation at a physiological nucleotide concentration (∼100 μm). Surprisingly, incorporation of T:T or C:T mismatches catalyzed by either H932Y or H932A mutants was followed by slow pyrophosphate release (or fast pyrophosphate rebinding). Also, H932Y readily catalyzed incorporation of multiple mismatches, which may have a profound physiological impact over time. His-932 is thought to contact the β-phosphate of the incoming nucleotide, so it is perhaps surprising that H932Y appears to slow rather than accelerate pyrophosphate release.
authors.affiliation: Department of Chemistry and Biochemistry, Institute of Cellular and Molecular Biology, University of Texas, Austin, Texas 78712, USA.
authors.forename: Dipanwita
authors.initials: D
authors.lastname: Batabyal
authors.forename: Jessica L
authors.initials: JL
authors.lastname: McKenzie
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Johnson
mesh_terms: D020137:Base Pair Mismatch; D002384:Catalysis; D003001:Cloning, Molecular; D004247:DNA / Q000737:chemistry; D004259:DNA-Directed DNA Polymerase / Q000737:chemistry*; D011756:Diphosphates / Q000737:chemistry; D054629:Genome, Mitochondrial; D006639:Histidine / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology*; D016296:Mutagenesis; D009154:Mutation; D009711:Nucleotides / Q000737:chemistry*; D010300:Parkinson Disease / Q000201:enzymology
chemical_list: D011756:Diphosphates; D009711:Nucleotides; D006639:Histidine; D004247:DNA; D004259:DNA-Directed DNA Polymerase