Mitochondrial aconitase is sensitive to oxidative inactivation and can aggregate and accumulate in many age-related disorders. Lon protease, an ATP-stimulated mitochondrial matrix protein, selectively recognizes and degrades the oxidized, hydrophobic form of aconitase after mild oxidative modification. The ATP-stimulated Lon protease may be an essential defence against the stress of life in an oxygen environment. By recognizing minor oxidative changes to protein structure and rapidly degrading the mildly modified protein, Lon protease may prevent extensive oxidation, aggregation and accumulation of aconitase, which could otherwise compromise mitochondrial function and cellular viability. Aconitase is probably only one of many mitochondrial matrix proteins that are preferentially degraded by Lon protease after oxidative modification.
The ATP-dependent Lon protease belongs to a unique group of proteases that bind DNA. human Lon binds specifically to a single-stranded GT-rich DNA sequence overlapping the light strand promoter of human mitochondrial DNA (mtDNA). Conformational changes in the Lon holoenzyme induced by nucleotide and protein substrate modulate the binding affinity for single-stranded mtDNA and RNA in vivo. Co-immunoprecipitation experiments show that Lon interacts with mtDNA polymerase γ and the Twinkle helicase, which are components of mitochondrial nucleoids.