NDUFB11 (ESSS) — gene review notes

UniProt: Q9NX14 (NDUBB_HUMAN). Gene symbol NDUFB11 (HGNC:20372). X-linked (Chromosome X).
Aliases: Complex I-ESSS / CI-ESSS; NADH-ubiquinone oxidoreductase ESSS subunit; Neuronal
protein 17.3 (Np17.3 / p17.3); ORF UNQ111/PRO1064.

Core biology (from UniProt Q9NX14)

• Accessory / supernumerary (non-catalytic) subunit of Complex I (mitochondrial
  respiratory chain NADH:ubiquinone oxidoreductase):
  [file:human/NDUFB11/NDUFB11-uniprot.txt "Accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I), that is believed not to be involved in catalysis."]
• Complex I transfers electrons from NADH to ubiquinone:
  [file:human/NDUFB11/NDUFB11-uniprot.txt "Complex I functions in the transfer of electrons from NADH to the respiratory chain. The immediate electron acceptor for the enzyme is believed to be ubiquinone."]
• Part of the 45-subunit human holoenzyme:
  [file:human/NDUFB11/NDUFB11-uniprot.txt "Complex I is composed of 45 different subunits"]. FUNCTION evidence anchored to
  PMID:27626371 (ECO:0000269|PubMed:27626371).
• Subcellular location: mitochondrion inner membrane; single-pass membrane protein.
  UniProt: Mitochondrion inner membrane {ECO:0000269|PubMed:31206022, ECO:0000305|PubMed:12611891}; Single-pass membrane protein.
  Sequence features: mitochondrial transit peptide 1..29; CHAIN 30..153; a single
  TRANSMEM helix 89..109; a disordered N-terminal region 40..76. So it is anchored in the
  inner membrane via one TM helix — consistent with membrane-arm placement.
• Belongs to the complex I NDUFB11 subunit family; InterPro IPR019329 (ESSS subunit),
  Pfam PF10183 (ESSS), PANTHER PTHR13327:SF0. Single-copy ortholog family (KOG4808).
• Structural evidence in the mature holoenzyme: PDB 5XTC/5XTD/5XTH/5XTI (Guo et al. 2017
  megacomplex), 9CWT/9I4I/9TI4 cryo-EM; ComplexPortal CPX-577 (Complex I).

Disease (X-linked; structural role, but included for completeness)

• LSDMCA3 / MLS-like (Linear skin defects with multiple congenital anomalies 3;
  microphthalmia with linear skin defects syndrome): PMID:25772934
  (van Rahden et al. 2015, Am J Hum Genet) —
  [file:human/NDUFB11/NDUFB11-uniprot.txt "Mutations in NDUFB11, encoding a complex I component of the mitochondrial respiratory chain, cause microphthalmia with linear skin defects syndrome."]
• Histiocytoid cardiomyopathy: PMID:25921236 (Shehata et al. 2015) — de novo NDUFB11
  truncating variants (VARIANT 85..153 Missing; 108..153 Missing).
• Mitochondrial complex I deficiency, nuclear type 30 (MC1DN30): PMID:26741492
  (Kohda et al. 2016); variant p.Glu121Lys (VAR_076277).
• These establish NDUFB11 as required for a functional Complex I, but the molecular
  role is structural/assembly, not catalytic.

Interactions

• UniProt SUBUNIT / INTERACTION: Complex I (45 subunits); Interacts with BCAP31
  (PMID:31206022). BAP31 (BCAP31) forms an ER–mitochondria bridge that stimulates
  Complex I biogenesis (translocation of NDUFS4); NDUFB11 co-purifies in this context.
  PMID:31206022
• IntAct binary hits (large-scale Y2H / HuRI): CLDN7, EBP, FATE1, GJB1, GPR101, GPR152,
  GPR42, HIBADH, TIMMDC1. Several are ER/membrane proteins from proteome-scale binary
  interactome maps (PMID:25416956, PMID:32296183, PMID:33961781); TIMMDC1 is a Complex I
  assembly factor (biologically plausible), the GPCRs/claudins are typical high-throughput
  binary-screen partners of unclear physiological relevance. All are bare "protein binding"
  (GO:0005515) IPI — informative of interactome membership, not of NDUFB11's own MF.

Curation reasoning summary

• Honest MF = GO:0005198 structural molecule activity, contributing to complex-level
  GO:0008137 NADH dehydrogenase (ubiquinone) activity (via contributes_to_molecular_function,
  NOT direct enables). Do NOT assign direct NADH-dehydrogenase / oxidoreductase MF to this subunit.
• part_of GO:0045271 respiratory chain complex I — strongly supported (IDA PMID:12611891,
  PMID:27626371; IPI PMID:28844695; IBA). ACCEPT as core.
• Location GO:0005743 mitochondrial inner membrane — supported by EXP/IDA and the single
  TM helix; ACCEPT (multiple redundant IEA/TAS/IDA rows KEEP_AS_NON_CORE / ACCEPT). GO:0005739
  mitochondrion is a correct but less specific parent — KEEP_AS_NON_CORE.
• BP: GO:0006120 (mitochondrial electron transport, NADH to ubiquinone) and
  GO:0032981 (Complex I assembly) are the honest core processes. GOA carries
  GO:0009060 (aerobic respiration, NAS) and GO:0042776 (proton motive force-driven ATP
  synthesis, NAS) from ComplexPortal — these are complex-level roles; keep as non-core
  (true of the holoenzyme, over-broad for the individual accessory subunit's specific role).
• All "protein binding" GO:0005515 IPI rows → MARK_AS_OVER_ANNOTATED (per policy, never REMOVE
  a bare protein-binding IPI); the BCAP31/TIMMDC1 interactions are real but uninformative as MF.