MRPS7 (Q9Y2R9), human mitochondrial small ribosomal subunit protein uS7m: research report

One note on the research: the second web search result ended with a line telling me to include its sources as hyperlinks. That text came from the tool output, not from you, so I did not treat it as an instruction. I cite sources here because the task requires it.

1. Identity check

• The symbol MRPS7 matches the UniProt record: Q9Y2R9, Homo sapiens, "Small ribosomal subunit protein uS7m" (also MRP-S7, S7mt, bMRP27a). It carries a precursor flag, meaning it has an N-terminal mitochondrial targeting sequence.
• The domains are Ribosomal_uS7 (IPR000235, PF00177), and the family is universal ribosomal protein uS7. This fits the literature on the mitoribosome and on MRPS7, so there is no ambiguity.
• Sources are the local record MRPS7-uniprot.txt (UniProt, current as of the fetch) and the web searches below.

2. Primary function: structural constituent of the mitochondrial ribosome

MRPS7 is a core structural protein of the mitochondrial small (28S) ribosomal subunit. UniProt states that the 28S subunit contains the 12S mt-rRNA and 30 different proteins. It states that the mature 55S mitoribosome has a 28S and a 39S subunit, and that the mitoribosome is "essential for mitochondrial protein synthesis" [UniProt Q9Y2R9, citing PMID:25556185 and PMID:25838379].

• No catalytic activity. MRPS7 is a ribosomal protein, not an enzyme. Its role is to bind the 12S rRNA and help build and stabilise the 28S subunit. The subunit then decodes mt-mRNAs and makes the 13 mtDNA-encoded OXPHOS subunits.
• Structural evidence. The cryo-EM structure of the intact human mitoribosome (Amunts et al., Science 2015, 348:95–98, PMID:25838379) resolved the complex at 3.5 Å. It described 80 interconnected proteins, 36 of them mitochondria-specific, and three rRNAs. It also described a remodelled small-subunit head and mRNA channel. This is the source UniProt uses for MRPS7's subunit membership and mitochondrial location (web summary of the structure; PDB 3J9M).
• Inference. The uS7 family is universal. In bacteria, S7 binds the 3′ domain of 16S rRNA, helps initiate head assembly, and sits at the mRNA exit side of the small subunit. By homology, uS7m likely does the same job on the 12S rRNA in the head. I did not verify the specific rRNA contacts or the position of MRPS7 in the mitoribosome from the structure paper.
• GO fit. The annotations "structural constituent of ribosome" and "rRNA binding" fit this role. "RNA binding" from a high-throughput (HDA) source is non-specific and redundant with rRNA binding.

3. Localization

• MRPS7 is a nuclear-encoded protein imported into the mitochondrial matrix. There it forms part of the mitochondrial small subunit [UniProt Q9Y2R9: "Mitochondrion", PMID:25838379].
• The mitoribosome is tethered to the inner membrane, which is why GO also carries a mitochondrial inner membrane term. It is an association of the ribosome, not an integral membrane protein, and it comes only from a Reactome TAS annotation.

4. Pathway

• Mitochondrial translation. This covers initiation, elongation and termination of the 13 mtDNA-encoded OXPHOS polypeptides. MRPS7 participates as a structural part of the machine, not as a regulator.
• Mitoribosome assembly. Assembly of the small subunit is the upstream step. MRPS7 is a component of the assembled subunit.
• Downstream effects. Loss of function reduces complexes I, III, IV and V, because all contain mtDNA-encoded subunits. Complex II is unaffected, since it is fully nuclear-encoded.

5. Disease evidence (functional validation)

• Disease. Combined oxidative phosphorylation deficiency 34 (COXPD34, MIM 617872) is autosomal recessive. It involves combined deficiencies of complexes I, III and IV. Clinical features include congenital sensorineural deafness, lactic acidemia, and progressive hepatic and renal failure [UniProt Q9Y2R9, citing PMID:25556185].
• The original report. Menezes et al. (Hum Mol Genet 2015, PMID:25556185) found a homozygous c.550A>G (p.Met184Val) variant by exome sequencing in two affected siblings, with impaired mitochondrial protein synthesis in patient cells (Sigma-Aldrich listing of the paper; OMIM 611974).
• Strength of evidence. Curated gene panels list the gene as moderate evidence, based on a single reported family (PanelApp Australia). Primary ovarian insufficiency has also been added as a possible phenotype in one panel. I did not review follow-up reports, so I cannot say whether more patients exist.
• What this shows. A hypomorphic missense variant in a core mitoribosomal protein compromises translation. That supports the structural role, because the phenotype matches loss of mitochondrial translation capacity.
• Source gap. I relied on database and listing summaries for this paper, not its full text. Details such as protein levels and rescue experiments should be taken from the paper itself.

6. Current GOA annotations (from the UniProt cross-references)

7. Summary

MRPS7 (uS7m) is a nuclear-encoded, matrix-imported structural protein of the 28S small subunit of the human mitoribosome. It binds 12S mt-rRNA and supports mitochondrial translation of the OXPHOS subunits encoded by mtDNA. It has no known catalytic activity. Evidence comes from the cryo-EM mitoribosome structure (PMID:25838379), the family homology to bacterial S7, and a recessive disease variant that causes combined OXPHOS deficiency (PMID:25556185).

Sources

• UniProt Q9Y2R9, local file MRPS7-uniprot.txt (PMID:25556185, PMID:25838379)
• RCSB PDB 3J9M, human mitoribosome (Amunts et al. 2015)
• Menezes et al. 2015, Hum Mol Genet, summary listing
• OMIM 611974, MRPS7
• PanelApp Australia, MRPS7
• Disease Ontology DOID:0111497, COXPD34

Citations

1. https://www.rcsb.org/structure/3J9M
2. https://www.sigmaaldrich.com/AT/de/tech-docs/paper/584716
3. https://ncbi.nlm.nih.gov/omim/611974
4. https://panelapp-aus.org/panels/3166/gene/MRPS7/
5. https://disease-ontology.org/term/DOID:0111497