The NDUFB6 protein weighs 15.5 kDa and is composed of 128 amino acids.[9][10] NDUFB6 is a subunit of the enzyme NADH dehydrogenase (ubiquinone), the largest of the respiratory complexes. The structure is L-shaped with a long, hydrophobictransmembrane domain and a hydrophilic domain for the peripheral arm that includes all the known redox centers and the NADH binding site.[8] It has been noted that the N-terminal hydrophobic domain has the potential to be folded into an 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 dehydrogenase (ubiquinone) complex at the inner mitochondrial membrane.[7]
The protein encoded by this gene is an accessory subunit of the multisubunit NADH:ubiquinone oxidoreductase (complex I) that is not directly involved in catalysis.[7] However, NDUFB6 is required for electron transfer activity.[11] Mammalian complex I is composed of 44 different subunits. It locates at the mitochondrial inner membrane. This protein complex has NADH dehydrogenase activity and oxidoreductase activity. It transfers electrons from NADH to the respiratory chain. The immediate electron acceptor for the enzyme is believed to be ubiquinone. Alternative splicing occurs at this locus and two transcript variants encoding distinct isoforms have been identified.[7] Initially, 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.[8]
Decreased expression of genes involved in oxidative phosphorylation, including NDUFB6, is associated with insulin resistance and type 2 diabetes. A polymorphism in the promoter region of the NDFUB6 gene resulting in an adenine to guanine shift at rs629566 was shown to create a DNA methylation site that is associated with a decline in NDUFB6 expression in muscle of aging patients.[12]
^"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^Emahazion T, Beskow A, Gyllensten U, Brookes AJ (Nov 1998). "Intron based radiation hybrid mapping of 15 complex I genes of the human electron transport chain". Cytogenetics and Cell Genetics. 82 (1–2): 115–9. doi:10.1159/000015082. PMID9763677. S2CID46818955.
^Smeitink J, Loeffen J, Smeets R, Triepels R, Ruitenbeek W, Trijbels F, van den Heuvel L (Aug 1998). "Molecular characterization and mutational analysis of the human B17 subunit of the mitochondrial respiratory chain complex I". Human Genetics. 103 (2): 245–50. doi:10.1007/s004390050813. PMID9760212. S2CID25046670.
^Loublier S, Bayot A, Rak M, El-Khoury R, Bénit P, Rustin P (Oct 2011). "The NDUFB6 subunit of the mitochondrial respiratory chain complex I is required for electron transfer activity: a proof of principle study on stable and controlled RNA interference in human cell lines". Biochemical and Biophysical Research Communications. 414 (2): 367–72. doi:10.1016/j.bbrc.2011.09.078. PMID21964293.
Loeffen JL, Triepels RH, van den Heuvel LP, Schuelke M, Buskens CA, Smeets RJ, Trijbels JM, Smeitink JA (Dec 1998). "cDNA of eight nuclear encoded subunits of NADH:ubiquinone oxidoreductase: human complex I cDNA characterization completed". Biochemical and Biophysical Research Communications. 253 (2): 415–22. doi:10.1006/bbrc.1998.9786. PMID9878551.
