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Reconstitution of a minimal mtDNA replisome in vitro
Jenny A Korhonen1, Xuan Hoi Pham, Mina Pellegrini
1Department of Medical Nutrition, Karolinska Institute, Novum, Huddinge, Sweden.
Abstract:
We here reconstitute a minimal mammalian mitochondrial DNA (mtDNA) replisome in vitro. The mtDNA polymerase (POLgamma) cannot use double-stranded DNA (dsDNA) as template for DNA synthesis. Similarly, the TWINKLE DNA helicase is unable to unwind longer stretches of dsDNA. In combination, POLgamma and TWINKLE form a processive replication machinery, which can use dsDNA as template to synthesize single-stranded DNA (ssDNA) molecules of about 2 kb. The addition of the mitochondrial ssDNA-binding protein stimulates the reaction further, generating DNA products of about 16 kb, the size of the mammalian mtDNA molecule. The observed DNA synthesis rate is 180 base pairs (bp)/min, corresponding closely to the previously calculated value of 270 bp/min for in vivo DNA replication. Our findings provide the first biochemical evidence that TWINKLE is the helicase at the mitochondrial DNA replication fork. Furthermore, mutations in TWINKLE and POLgamma cause autosomal dominant progressive external ophthalmoplegia (adPEO), a disorder associated with deletions in mitochondrial DNA. The functional interactions between TWINKLE and POLgamma thus explain why mutations in these two proteins cause an identical syndrome.
Insights
Researchers reconstituted a minimal mammalian mitochondrial DNA (mtDNA) replisome in vitro. This study identifies TWINKLE as the mtDNA replication fork helicase, explaining its link to progressive external ophthalmoplegia.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Mammalian mitochondrial DNA (mtDNA) replication is crucial for cellular energy production.
- The precise mechanisms and protein components of the mtDNA replisome are not fully elucidated.
- mtDNA polymerase (POLgamma) and TWINKLE helicase are known to be involved in mtDNA maintenance.
Purpose of the Study:
- To reconstitute a minimal mammalian mtDNA replisome in vitro.
- To biochemically characterize the roles of POLgamma and TWINKLE in mtDNA replication.
- To establish the functional relationship between TWINKLE, POLgamma, and associated diseases.
Main Methods:
- In vitro biochemical reconstitution of the mammalian mtDNA replisome.
- Assays to determine DNA synthesis activity of POLgamma and TWINKLE.
- Analysis of the effect of mitochondrial ssDNA-binding protein on replication.
Main Results:
- POLgamma and TWINKLE form a processive replication machinery capable of synthesizing ssDNA from dsDNA templates.
- The addition of mitochondrial ssDNA-binding protein significantly increases DNA product size.
- The in vitro DNA synthesis rate closely matches in vivo estimates, supporting TWINKLE's role as the replication helicase.
Conclusions:
- TWINKLE is biochemically confirmed as the helicase at the mitochondrial DNA replication fork.
- The functional interaction between TWINKLE and POLgamma explains the shared pathology of autosomal dominant progressive external ophthalmoplegia (adPEO).
- This study provides critical insights into the molecular basis of mtDNA replication and associated disorders.
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