NDUFB9

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Protein-coding gene in the species Homo sapiens

title: "NDUFB9" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["human-proteins"] description: "Protein-coding gene in the species Homo sapiens" topic_path: "general/human-proteins" source: "https://en.wikipedia.org/wiki/NDUFB9" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Protein-coding gene in the species Homo sapiens ::

NADH dehydrogenase [ubiquinone] 1 beta subcomplex subunit 9 is an enzyme that in humans is encoded by the NDUFB9 gene. It belongs to the superfamily of LYRM proteins, which are characterized by a conserved leucine–tyrosine–arginine motif. NADH dehydrogenase (ubiquinone) 1 beta subcomplex subunit 9 is an accessory subunit of the NADH dehydrogenase (ubiquinone) complex, located in the mitochondrial inner membrane. It is also known as Complex I and is the largest of the five complexes of the electron transport chain.

Structure

The NDUFB9 gene is located on the q arm of chromosome 8 in position 13.3 and is 10,884 base pairs long. The NDUFB9 protein weighs 22 kDa and is composed of 179 amino acids. NDUFB9 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. 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.

Function

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. Mammalian complex I is composed of 45 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. 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.

Clinical significance

A mutation in NDUFB9 resulting in reduction in NDUFB9 protein and both amount and activity of complex I has been shown to be a causal mutation leading to Complex I deficiency.

References

References

  1. (Sep 1996). "The human B22 subunit of the NADH-ubiquinone oxidoreductase maps to the region of chromosome 8 involved in branchio-oto-renal syndrome". Genomics.
  2. "Entrez Gene: NDUFB9 NADH dehydrogenase (ubiquinone) 1 beta subcomplex, 9, 22kDa".
  3. (May 2024). "Installation of LYRM proteins in early eukaryotes to regulate the metabolic capacity of the emerging mitochondrion". Open Biology.
  4. (2013). "Fundamentals of biochemistry: life at the molecular level". Wiley.
  5. (Oct 2013). "Integration of cardiac proteome biology and medicine by a specialized knowledgebase". Circulation Research.
  6. (July 2025). "NADH dehydrogenase [ubiquinone] 1 beta subcomplex subunit 9 }}{{Dead link". Cardiac Organellar Protein Atlas Knowledgebase (COPaKB).
  7. (February 2012). "Mutation screening of 75 candidate genes in 152 complex I deficiency cases identifies pathogenic variants in 16 genes including NDUFB9". Journal of Medical Genetics.

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human-proteins