Abstract
The human mitochondrial heat shock protein 60 (hsp60) is a tetradecameric chaperonin that folds proteins in the mitochondrial matrix. An hsp60 D3G mutation leads to MitCHAP-60, an early onset neurodegenerative disease while hsp60 V72I has been linked to SPG13, a form of hereditary spastic paraplegia. Previous studies have suggested that these mutations impair the protein folding activity of hsp60 complexes but the detailed mechanism by which these mutations lead the neuromuscular diseases remains unknown. It is known, is that the β-subunit of the human mitochondrial ATP synthase co-immunoprecipitates with hsp60 indicating that the β-subunit is likely a substrate for the chaperonin. Therefore, we hypothesized that hsp60 mutations cause misfolding of proteins that are critical for aerobic respiration. Negative-stain electron microscopy and DLS results suggest that the D3G and V72I complexes fall apart when treated with ATP or ADP and are therefore unable to fold denatured substrates such as α-lactalbumin, malate dehydrogenase (MDH), and the β-subunit of ATP synthase in in-vitro protein-folding assays. These data suggests that hsp60 plays a crucial role in folding important players in aerobic respiration such as the β-subunit of the ATP synthase. The hsp60 mutations D3G and V72I impair its ability to fold mitochondrial substrates leading to abnormal ATP synthesis and the development of the MitCHAP-60 and SPG13 neuromuscular degenerative disorders.
Highlights
MitCHAP-60 is an early-onset neurodegenerative disease inherited in an autosomal-recessive pattern characterized by neuronal hypomyelination and leukodystrophy[16]
Previous studies have demonstrated that the disease-causing D3G and V72I mutations reduce the chaperonin ATP hydrolysis activity and subsequent protein folding ability of the resultant hsp[60] complexes both in-vitro and in-vivo[17,19]
We investigated the molecular mechanism by which the hsp[60] mutations lead to the MitCHAP-60 and SPG13
Summary
MitCHAP-60 is an early-onset neurodegenerative disease inherited in an autosomal-recessive pattern characterized by neuronal hypomyelination and leukodystrophy (brain white matter degradation)[16]. MitCHAP-60 usually leads to death within the first two decades of life[16] Both SPG13 and MitCHAP-60 have been linked to point mutations in hsp[60]. Previous studies have demonstrated that the disease-causing D3G and V72I mutations reduce the chaperonin ATP hydrolysis activity and subsequent protein folding ability of the resultant hsp[60] complexes both in-vitro and in-vivo[17,19]. Due to the labile nature of hsp60/10 complexes, these studies had to reconstitute the expressed hsp[60] proteins to form tetradecameric rings. Negative-stain electron microscopy along with DLS results suggest that the D3G and V72I complexes fall apart when treated with ATP or ADP and impair their ability to fold mitochondrial substrate proteins
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