title: Structure-function defects of the twinkle amino-terminal region in progressive external ophthalmoplegia.
abstract: TWINKLE is a DNA helicase needed for mitochondrial DNA replication. In lower eukaryotes the protein also harbors a primase activity, which is lost from TWINKLE encoded by mammalian cells. Mutations in TWINKLE underlie autosomal dominant progressive external ophthalmoplegia (adPEO), a disorder associated with multiple deletions in the mtDNA. Four different adPEO-causing mutations (W315L, K319T, R334Q, and P335L) are located in the N-terminal domain of TWINKLE. The mutations cause a dramatic decrease in ATPase activity, which is partially overcome in the presence of single-stranded DNA. The mutated proteins have defects in DNA helicase activity and cannot support normal levels of DNA replication. To explain the phenotypes, we use a molecular model of TWINKLE based on sequence similarities with the phage T7 gene 4 protein. The four adPEO-causing mutations are located in a region required to bind single-stranded DNA. These mutations may therefore impair an essential element of the catalytic cycle in hexameric helicases, i.e. the interplay between single-stranded DNA binding and ATP hydrolysis.
authors.affiliation: Department of Laboratory Medicine, Division of Metabolic Diseases, Karolinska Institutet, Novum, SE-141 86 Stockholm, Sweden.
authors.forename: Teresa
authors.initials: T
authors.lastname: Holmlund
authors.forename: Géraldine
authors.initials: G
authors.lastname: Farge
authors.forename: Vineet
authors.initials: V
authors.lastname: Pande
authors.forename: Jenny
authors.initials: J
authors.lastname: Korhonen
authors.forename: Lennart
authors.initials: L
authors.lastname: Nilsson
authors.forename: Maria
authors.initials: M
authors.lastname: Falkenberg
mesh_terms: D000595:Amino Acid Sequence; D004265:DNA Helicases / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D004261:DNA Replication / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D017246:Ophthalmoplegia, Chronic Progressive External / Q000201:enzymology* / Q000235:genetics; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D004272:DNA, Mitochondrial; D011994:Recombinant Proteins; D004265:DNA Helicases