NDUFB7 (B18) — review notes

UniProt: P17568 (NDUB7_HUMAN). HGNC:7702. Gene ID 4713. NCBI taxon 9606.

Identity / naming

NADH dehydrogenase [ubiquinone] 1 beta subcomplex subunit 7; aka Complex I-B18 / CI-B18,
NADH-ubiquinone oxidoreductase B18 subunit, and (historically) "Cell adhesion protein SQM1"
from an early cDNA-cloning report PMID:2302251. The "cell adhesion" naming is a legacy of the
original cloning; the protein's established function is as a Complex I accessory subunit.
[file:human/NDUFB7/NDUFB7-uniprot.txt "AltName: Full=Cell adhesion protein SQM1"]

Accessory (supernumerary) subunit of mitochondrial respiratory chain Complex I
(NADH:ubiquinone oxidoreductase), not involved in catalysis.
[file:human/NDUFB7/NDUFB7-uniprot.txt "Accessory subunit of the mitochondrial membrane respiratory"
... "that is believed not to be" (involved in catalysis)]
Complex I transfers electrons from NADH to ubiquinone; the immediate electron acceptor is ubiquinone.
[file:human/NDUFB7/NDUFB7-uniprot.txt "Complex I functions in the transfer of electrons"]
Complex I is composed of 45 different subunits.
[file:human/NDUFB7/NDUFB7-uniprot.txt "Complex I is composed of 45 different subunits"]
Subcellular location: Mitochondrion inner membrane (peripheral membrane protein);
Mitochondrion intermembrane space.
[file:human/NDUFB7/NDUFB7-uniprot.txt "Mitochondrion inner membrane" / "Mitochondrion intermembrane space"]
Twin-CX9C: contains two C-X9-C motifs (residues 59-69 and 80-90) forming a helix-coil-helix (CHCH)
domain (56-98) with two intramolecular disulfide bonds (Cys59-Cys90, Cys69-Cys80); imported/oxidatively
folded via the MIA40 (CHCHD4) disulfide relay of the IMS.
[file:human/NDUFB7/NDUFB7-uniprot.txt "Contains two C-X9-C motifs that are predicted to form a helix-"]
N-terminal N-myristoyl glycine lipid modification at residue 2 (INIT_MET removed).
[file:human/NDUFB7/NDUFB7-uniprot.txt "N-myristoyl glycine"]
SIMILARITY: complex I NDUFB7 subunit family. Structures: 5XTC/5XTD/5XTH, 9CWT, 9I4I, 9TI4 (cryo-EM).

IMS-surface localization — NDUFB7 and NDUFA8 localize to the intermembrane-space surface of
Complex I; Cx9C subunits proposed to stabilize the membrane domain via intramolecular disulfides.
PMID:21310150
(This paper's title/abstract is explicitly about NDUFB7 — HIGH relevance, VERIFIED.)
Complex membership (MS) — identified as a subunit by immunopurification + MS of human Complex I.
PMID:12611891
Complex membership (structure) — cryo-EM of human megacomplex I2III2IV2 assigns individual CI subunits.
PMID:28844695
Accessory-subunit importance — systematic accessory-subunit KO/proteomics: accessory subunits are
integral for assembly and function; loss destabilizes co-module subunits.
PMID:27626371
Disease (MC1DN39) — biallelic intronic variant c.113-10C>G reduced NDUFB7 protein and reduced
Complex I activity; WT-NDUFB7 complementation normalized CI function. Congenital lactic acidosis +
hypertrophic cardiomyopathy, fatal.
PMID:33502047
This IMP demonstrates NDUFB7 is REQUIRED for holoenzyme activity — not that the subunit itself
catalyzes NADH dehydrogenase activity.

MF: honest subunit-level MF is GO:0005198 structural molecule activity.
The complex-level catalytic activity GO:0008137 (NADH dehydrogenase (ubiquinone) activity) is
recorded via contributes_to_molecular_function (NOT direct enables).
Both direct enables GO:0008137 annotations (IMP PMID:33502047; NAS PMID:9878551) →
MARK_AS_OVER_ANNOTATED (non-catalytic accessory subunit; per policy IMP is not REMOVEd).
BP core: GO:0006120 (electron transport, NADH→ubiquinone) ACCEPT; plus GO:0032981
(mitochondrial respiratory chain complex I assembly) added to core_functions (assembly role).
GO:0009060 aerobic respiration (NAS) → KEEP_AS_NON_CORE (correct but general).
GO:0042776 ATP synthesis (NAS) and GO:1902600 proton transmembrane transport (IEA) →
MARK_AS_OVER_ANNOTATED (downstream / core-membrane-subunit-driven, not this subunit).
CC: part_of GO:0045271 (respiratory chain complex I) ACCEPT (IDA/IPI/IBA); captured as in_complex.
GO:0005743 inner membrane and GO:0005758 IMS ACCEPT (experimental); captured in locations.
GO:0005739 mitochondrion (IEA/HTP/HDA) and redundant Reactome-TAS inner-membrane rows → KEEP_AS_NON_CORE.
MF protein binding (GO:0005515, IPI, PMID:32296183 HuRI + PMID:32814053 ND interactome):
both are high-throughput Y2H against non-Complex-I partners → MARK_AS_OVER_ANNOTATED
(uninformative bare "protein binding"; not REMOVEd per policy).

All cited publications in publications/PMID_*.md are abstract-only (full_text_available: false)
except PMID:32296183, PMID:20833797, PMID:34800366. All supporting_text quotes were grep-verified
as verbatim single-line substrings of their source.
No deep-research file generated (per instruction; falcon out of credits).