Human Endonuclease G Preferentially Cleaves Oxidatively Damaged DNA

Area of Science:

• Mitochondrial biology
• DNA repair mechanisms
• Enzymology

Background:

• Endonuclease G (EndoG) is vital for mitochondrial DNA (mtDNA) maintenance and removal of DNA during apoptosis.
• The specific substrates and cleavage preferences of EndoG are not fully understood.
• Oxidative stress poses a significant threat to mtDNA integrity.

Purpose of the Study:

• To characterize the substrate specificity and cleavage preferences of human EndoG (hEndoG).
• To elucidate the role of hEndoG in response to oxidative DNA damage.
• To provide structural insights into hEndoG-nucleic acid interactions.

Main Methods:

• Biochemical assays to test hEndoG activity on various nucleic acid substrates (ssDNA, dsDNA, modified DNA, RNA/DNA hybrids).
• Analysis of cleavage preferences on nicked, gapped, and oxidatively modified DNA.
• Structural modeling of hEndoG bound to DNA substrates.

Main Results:

• hEndoG exhibits modest binding affinities across diverse substrates but shows a strong preference for damaged DNA.
• hEndoG preferentially cleaves oxidatively damaged DNA, including nicked/gapped dsDNA and 8-oxoguanine DNA (oxoG-DNA).
• Cleavage occurs opposite nicks/gaps and targets the strand complementary to modified bases in oxoG-DNA and 5-hydroxymethylated cytosine DNA (5hmC-DNA).

Conclusions:

• hEndoG plays a critical role in removing oxidatively damaged DNA, thereby preserving mitochondrial genome integrity.
• The enzyme's preference for damaged substrates highlights its importance in cellular defense against oxidative stress.
• Structural flexibility of ssDNA contributes to hEndoG's substrate binding and catalytic activity.