FH

Frataxin is a monomeric mitochondrial protein that is believed to be involved in iron homeostasis through an unknown mechanism. Expression of frataxin is highest in tissue rich with mitochondria including liver, heart, and skeletal muscle (Campuzano, 1996; Koutnikova, 1997). Frataxin is expressed as a 30 kDa precursor (transient; 210 amino acids) that is processed within in the mitochondria in two steps catalysed by the mitochondrial processing peptidase (MPP) to yield the mature protein (Koutnikova, 1998). The first step involves cleavage of the first 41 N-terminal amino acids by MPP yielding a transient intermediate of approximately 20 kDa (aa 42-210). Further cleavage of the N-terminus of this 20 kDa intermediate by MPP results in the mature 18 kDa frataxin protein (aa 56-210). Defects in the gene encoding frataxin are implicated as the cause of Friedreich's ataxia, an autosomal recessive, progressive degenerative disease characterized by neurodegeneration and cardiomyopathy. In the majority of cases of Friedreich's ataxia, there is an expansion of a trinucleotide repeat in the first intron of the gene encoding frataxin resulting in a marked decrease in frataxin expression, perhaps due to the formation of some unusual yet stable DNA structure that interferes with transcription (Campuzano, 1997; Bidichandani, 1998). This reduction in frataxin expression results in the accumulation of unchelated iron in the mitochondria, inhibition of mitochondrial iron-sulfer proteins, and iron mediated oxidative stress (Foury, 1997; for review see Puccio, 2000).

FH; fumarate hydratase; fumarate hydratase, mitochondrial; fumarase; MCL; LRCC; HLRCC; MCUL1;