NDUFA3

NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 3 is a is_associated_with::protein that in humans is encoded by the NDUFA3 is_associated_with::gene. The NDUFA3 protein is a subunit of is_associated_with::NADH dehydrogenase (ubiquinone), which is located in the is_associated_with::mitochondrial inner membrane and is the largest of the five complexes of the is_associated_with::electron transport chain.

Structure
The NDUFA3 gene is located on the q arm of is_associated_with::chromosome 19 at position 13.42, and it has a total span of 4,123 base pairs. The NDUFA3 gene produces an 11 kDa protein composed of 99 is_associated_with::amino acids. NDUFA3 is a subunit of the enzyme is_associated_with::NADH dehydrogenase (ubiquinone), the largest of the respiratory complexes. The structure is L-shaped with a long, is_associated_with::hydrophobic is_associated_with::transmembrane domain and a is_associated_with::hydrophilic domain for the peripheral arm that includes all the known redox centers and the NADH binding site. NDUFA3 is one of about 31 hydrophobic subunits that form the transmembrane region of Complex I. It has been noted that the N-terminal hydrophobic domain has the potential to be folded into an is_associated_with::alpha helix spanning the inner mitochondrial membrane with a C-terminal hydrophilic domain interacting with globular subunits of Complex I. The highly conserved two-domain structure suggests that this feature is critical for the protein function and that the hydrophobic domain acts as an anchor for the NADH:ubiquinone is_associated_with::oxidoreductase complex at the inner mitochondrial membrane.

Function
The human NDUFA3 gene codes for a subunit of Complex I of the respiratory chain, which transfers electrons from NADH to is_associated_with::ubiquinone. However, NDUFA3 is an accessory subunit of the complex that is believed not to be involved in catalysis. Initially, is_associated_with::NADH binds to Complex I and transfers two electrons to the is_associated_with::isoalloxazine ring of the is_associated_with::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 is_associated_with::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.

Interactions
NDUFA3 has been shown to interact with is_associated_with::ubiquitin C, a polyubiquitin precursor.