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Efficient repair of abasic sites in DNA by mitochondrial enzymes
1Department of Pharmacological Sciences, State University of New York at Stony Brook, 11794-8651, USA.
Abstract:
Mutations in mitochondrial DNA (mtDNA) cause a variety of relatively rare human diseases and may contribute to the pathogenesis of other, more common degenerative diseases. This stimulates interest in the capacity of mitochondria to repair damage to mtDNA. Several recent studies have shown that some types of damage to mtDNA may be repaired, particularly if the lesions can be processed through a base excision mechanism that employs an abasic site as a common intermediate. In this paper, we demonstrate that a combination of enzymes purified from Xenopus laevis mitochondria efficiently repairs abasic sites in DNA. This repair pathway employs a mitochondrial class II apurinic/apyrimidinic (AP) endonuclease to cleave the DNA backbone on the 5' side of an abasic site. A deoxyribophosphodiesterase acts to remove the 5' sugar-phosphate residue left by AP endonuclease. mtDNA polymerase gamma fills the resulting 1-nucleotide gap. The remaining nick is sealed by an mtDNA ligase. We report the first extensive purification of mtDNA ligase as a 100-kDa enzyme that functions with an enzyme-adenylate intermediate and is capable of ligating oligo(dT) strands annealed to poly(rA). These properties together with preliminary immunological evidence suggest that mtDNA may be related to nuclear DNA ligase III.
Insights
Mitochondrial DNA (mtDNA) repair is crucial for preventing disease. Researchers identified a pathway using specific enzymes to efficiently repair abasic sites in mtDNA, offering insights into mtDNA maintenance.
Area of Science:
- Biochemistry
- Molecular Biology
- Genetics
Background:
- Mitochondrial DNA (mtDNA) mutations are linked to human diseases.
- Understanding mtDNA repair mechanisms is vital for disease pathogenesis research.
- Base excision repair pathways involving abasic sites are implicated in mtDNA damage repair.
Purpose of the Study:
- To investigate the capacity of mitochondrial enzymes to repair abasic sites in DNA.
- To characterize the enzymes involved in a potential mtDNA repair pathway.
- To purify and analyze mitochondrial DNA ligase.
Main Methods:
- Purification of enzymes from Xenopus laevis mitochondria.
- Biochemical assays to assess abasic site repair.
- Characterization of purified mitochondrial DNA ligase activity.
- Preliminary immunological analysis of mtDNA ligase.
Main Results:
- A combination of purified mitochondrial enzymes efficiently repairs abasic sites in DNA.
- The repair pathway involves a mitochondrial class II AP endonuclease, a deoxyribophosphodiesterase, mtDNA polymerase gamma, and mtDNA ligase.
- Mitochondrial DNA ligase was extensively purified as a 100-kDa enzyme.
- The purified mtDNA ligase utilizes an enzyme-adenylate intermediate and ligates DNA strands.
Conclusions:
- Xenopus laevis mitochondrial enzymes can efficiently repair abasic sites in DNA.
- A specific multi-enzyme pathway for mtDNA repair has been elucidated.
- Mitochondrial DNA ligase shares properties with nuclear DNA ligase III, suggesting a potential relationship.