Structure-function defects of the twinkle amino-terminal region in progressive external ophthalmoplegia.
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.
Holmlund
Teresa
T
Department of Laboratory Medicine, Division of Metabolic Diseases, Karolinska Institutet, Novum, SE-141 86 Stockholm, Sweden.
Farge
Géraldine
G
Pande
Vineet
V
Korhonen
Jenny
J
Nilsson
Lennart
L
Falkenberg
Maria
M
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
D004272:DNA, Mitochondrial; D011994:Recombinant Proteins; D004265:DNA Helicases