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Complex I and the cAMP cascade in human physiopathology
S Papa1, S Scacco, A M Sardanelli
1Department of Medical Biochemistry and Biology, University of Bari, Italy. papabchm@cimedoc.uniba.it
Abstract:
A cAMP-dependent protein kinase (PKA) is localized in mammalian mitochondria with the catalytic site at the matrix side of the membrane where it phosphorylates a number of proteins. One of these is the 18 kDa(IP) subunit of the mammalian complex I of the respiratory chain, encoded by the nuclear NDUFS4 gene. Mitochondria have a Ca(2+)-inhibited phosphatase, which dephosphorylates the 18 kDa phosphoprotein of complex I. In fibroblast and myoblast cultures cAMP-dependent phosphorylation of the 18 kDa protein is associated with stimulation of complex I and overall respiratory activity with NAD-linked substrates. Mutations in the human NDUFS4 gene have been found, which in the homozygous state are associated with deficiency of complex I and fatal neurological syndrome.
Insights
Mitochondrial cAMP-dependent protein kinase (PKA) phosphorylates Complex I, enhancing respiratory activity. Mutations in the NDUFS4 gene linked to Complex I deficiency cause fatal neurological disorders.
Area of Science:
- Mitochondrial biochemistry
- Cellular respiration
- Molecular genetics
Background:
- Mitochondria contain cAMP-dependent protein kinase (PKA) that phosphorylates proteins on the matrix side of the inner membrane.
- Complex I of the respiratory chain includes an 18 kDa subunit (encoded by NDUFS4) that is a substrate for mitochondrial PKA.
- Mitochondria possess a Ca(2+)-inhibited phosphatase that dephosphorylates this 18 kDa subunit.
Purpose of the Study:
- To investigate the role of cAMP-dependent phosphorylation of the 18 kDa subunit of Complex I in regulating mitochondrial respiratory activity.
- To explore the functional consequences of NDUFS4 gene mutations associated with Complex I deficiency.
Main Methods:
- Studies were conducted using fibroblast and myoblast cell cultures.
- Assessed the impact of cAMP-dependent phosphorylation on Complex I activity and overall respiratory function with NAD-linked substrates.
Main Results:
- cAMP-dependent phosphorylation of the 18 kDa protein was associated with increased Complex I activity.
- This phosphorylation event correlated with enhanced overall respiratory activity when using NAD-linked substrates.
- Mutations in the human NDUFS4 gene, when homozygous, lead to Complex I deficiency and a fatal neurological syndrome.
Conclusions:
- Mitochondrial PKA-mediated phosphorylation of the NDUFS4-encoded 18 kDa subunit is a regulatory mechanism for Complex I and cellular respiration.
- Dysfunction of this regulatory pathway, as seen in NDUFS4 mutations, can result in severe mitochondrial disease and neurological impairment.