J7SF87 (sqrd-2, Y9C9A.16b) manual literature review

No deep-research API was available, so this review was assembled by hand from the cached
publications and a PubMed search ("(sqrd-2 OR sqrd-1 OR sulfide quinone oxidoreductase) AND
elegans", 5 hits), plus a sequence comparison in J7SF87-bioinformatics/.

Identity

• UniProtKB J7SF87 (TrEMBL, unreviewed) is the 422-residue Y9C9A.16b product of WormBase gene
  WBGene00021183 (GeneID 189421), chromosome IV. The shorter Y9C9A.16a product is Q9N2S1 (361 aa).
• The gene was named sqrd-2 by Mikolas et al.: PMID:23484030
• It is the paralog of sqrd-1 (F02H6.5). Budde and Roth: PMID:21840852
• It is expressed: PMID:39178951

Sequence (J7SF87-bioinformatics/RESULTS.md)

• 45.3% identical to human SQOR (Q9Y6N5); both catalytic persulfide cysteines (human Cys201 and
  Cys379) are conserved, as J7SF87 Cys169 and Cys351; the FAD-binding positions and the N-terminal
  GxGxxG motif (residue 18) are present.
• No counterpart of the human N-terminal transit peptide: the J7SF87 model starts 17 residues
  before the GxGxxG motif.
• Q9N2S1 (isoform a) lacks residues 1-61, including the FAD motif, but keeps both cysteines.
• 75.1% identical to SQRD-1 (C6KRP5).

Genetics and physiology

• A deletion allele does not cause H2S sensitivity: PMID:21840852
• In liquid sulfide, sqrd-2(ok3440) recovers motility slightly earlier than wild type:
  PMID:39178951. The authors speculate:
  PMID:39178951.
• Expression is not induced by H2S, unlike sqrd-1: PMID:39178951
• Homology models of SQRD-2 dock ubiquinone and rhodoquinone in the quinone site (in silico only):
  PMID:39178951
• Expression rises 7.6-fold in gei-8 (NCoR/SMRT homologue) mutants: PMID:23484030. RNAi has no phenotype in wild type
  PMID:23484030, but modifies gei-8 gonad phenotypes. The dsRNA region includes three 21U-RNA
  loci, so the phenotypes cannot be assigned to the protein.

Ortholog biochemistry

• Human SQOR is the mitochondrial glutathione-dependent SQR (EC 1.8.5.8), whose catalytic
  cysteines are experimentally defined (UniProt Q9Y6N5 ACT_SITE 201 and 379, PubMed:30905673).

Not found

• No enzyme assay, purified protein, localization study or structure of worm SQRD-2.