NDUFA9

Structure

The NDUFA9 gene is located on the p arm of chromosome 12 in position 13.3 and spans 45,222 base pairs. The gene produces a 42.5 kDa protein composed of 377 amino acids. NDUFA9 is a subunit of the enzyme NADH dehydrogenase (ubiquinone), the largest of the respiratory complexes. The structure is L-shaped with a long, hydrophobic transmembrane domain and a hydrophilic domain for the peripheral arm that includes all the known redox centers and the NADH binding site. The predicted secondary structure is primarily alpha helix, but the carboxy-terminal half of the protein has high potential to adopt a coiled-coil form. The amino-terminal part contains a putative beta sheet rich in hydrophobic amino acids that may serve as mitochondrial import signal.

Function

The human NDUFA9 gene codes for a subunit of Complex I of the respiratory chain, which transfers electrons from NADH to ubiquinone. NADH binds to Complex I and transfers two electrons to the isoalloxazine ring of the flavin mononucleotide (FMN) prosthetic arm to form FMNH2. The electrons are transferred through a series of iron-sulfur (Fe-S) clusters in the prosthetic arm and finally to coenzyme Q10 (CoQ), which is reduced to ubiquinol (CoQH2). The flow of electrons changes the redox state of the protein, resulting in a conformational change and pK shift of the ionizable side chain, which pumps four hydrogen ions out of the mitochondrial matrix.

Clinical significance

Decreased expression of NDUFA9 is associated with Leigh's syndrome, a severe neurological disorder that typically arises in the first year of life, is characterized by progressive loss of mental and movement abilities, and typically results in death within a couple of years, usually due to respiratory failure. A mutation in the MT-ND3 gene (tyrosine to cytosine at the 10191 position) results in a substitution of serine for proline, which may introduce instability of Complex I due to the inability form subcomplexes between MT-ND3 and NDUFA9. However, this genetic identification may not be suitable for prenatal testing because of the mutation's age and tissue dependence.

Interactions

NDUFA9 has been shown to have 135 binary protein-protein interactions including 112 co-complex interactions. NDUFA9 appears to interact with BLOC1S1, NDUFS1, NOA1, CYSRT1, KRTAP6-2, CIAO1, MT-ND3, TSC22D1, DNAJA3, SIRT3, MAGED1, and SSR1.

References

References

1. "Entrez Gene: NDUFA9 NADH dehydrogenase (ubiquinone) 1 alpha subcomplex, 9".
2. (April 1993). "Construction and evaluation of a hncDNA library of human 12p transcribed sequences derived from a somatic cell hybrid". Genomics.
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5. (Nov 1998). "Intron based radiation hybrid mapping of 15 complex I genes of the human electron transport chain". Cytogenetics and Cell Genetics.
6. (August 2005). "Fulminant neurological deterioration in a neonate with Leigh syndrome due to a maternally transmitted missense mutation in the mitochondrial ND3 gene". Biochemical and Biophysical Research Communications.
7. (October 2013). "Integration of cardiac proteome biology and medicine by a specialized knowledgebase". Circulation Research.
8. "NDUFA9 - NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 9". Cardiac Organellar Protein Atlas Knowledgebase (COPaKB).
9. "NDUFA9 - NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 9, mitochondrial". The UniProt Consortium.
10. (December 1997). "Identification and primary structure of five human NADH-ubiquinone oxidoreductase subunits". Biochemical and Biophysical Research Communications.
11. "135 binary interactions found for search term NDUFA9". EMBL-EBI.