GATC (UniProt O43716), human mitochondrial glutamyl-tRNA(Gln) amidotransferase subunit C

0. Identity check

• The symbol GATC is the HGNC symbol for the human glutamyl-tRNA(Gln) amidotransferase subunit C (Glu-AdT subunit C, hGatC, formerly 15E1.2). It is not the "GATC" DNA motif used in Dam methylation or restriction-site literature, and it is not a different gene.
• The UniProt record (O43716) gives the family as GatC and the domains as GatC (PF02686, IPR003837) and Asp/Glu-ADT_sf_sub_c (IPR036113). The record is a mitochondrial precursor.
• The symbol is ambiguous with the DNA tetranucleotide. The literature below is for the protein.
• Evidence limits: I had no access to the cached publications/ files or to the full texts. Statements below come from the UniProt header text supplied in the prompt and from web search summaries. I did not check the quotes verbatim, so they should not be used as supporting_text without checking.

1. Primary function

GATC is the smallest, non-catalytic subunit of the heterotrimeric mitochondrial GatCAB complex. The other two subunits are QRSL1 (GatA) and GATB.

• Why the complex is needed. Mitochondria have no glutaminyl-tRNA synthetase. Mitochondrial tRNA(Gln) is first mischarged with glutamate by the mitochondrial glutamyl-tRNA synthetase (EARS2). GatCAB then converts the Glu-tRNA(Gln) to Gln-tRNA(Gln) by transamidation.
• Reaction: Glu-tRNA(Gln) + L-glutamine + ATP → Gln-tRNA(Gln) + L-glutamate + ADP + Pi.
• GatA (QRSL1) supplies the glutamine amidase activity. GatB (GATB) activates the Glu-tRNA with ATP and carries the transamidase function. GatC stabilises the complex and acts as a scaffold between them.
• Evidence for the pathway. Nagao et al. 2009, "Biogenesis of glutaminyl-mt tRNAGln in human mitochondria", PNAS (PMID:19805282). The UniProt record cites this paper for the "hGatC" name, and it is the source for the human indirect Gln-mt-tRNA pathway.
• From memory, which I could not check here, it showed that human GatA, GatB and GatC form the complex and are all needed to make Gln-mt-tRNA(Gln).
• Web search could not retrieve this paper, so the details are unconfirmed.
• Evidence from patients. Friederich et al. 2018, Nat Commun, "Pathogenic variants in glutamyl-tRNAGln amidotransferase subunits cause a lethal mitochondrial cardiomyopathy disorder" (PMID:30283131, doi:10.1038/s41467-018-06250-w; abstract and mirrors).
• The paper describes nine patients from five families with defects in QRSL1, GATB or GATC and a lethal metabolic cardiomyopathy.
• Patient fibroblasts had combined respiratory chain deficiencies. Charging of mt-tRNAGln and mitochondrial translation were impaired without glutamine and recovered with high glutamine.
• Lentiviral rescue and yeast homolog models supported pathogenicity.
• I did not retrieve the specific GATC variants or how many patients carried them.
• Disease link. Biallelic GATC variants are listed as combined oxidative phosphorylation deficiency 42 (COXPD42, MIM:617210; see the dismech entry). It is a lethal infantile mitochondrial cardiomyopathy. I did not confirm the MIM number independently.

2. Localization

The protein has a mitochondrial targeting presequence, which is why UniProt lists it as a precursor. It acts in the mitochondrial matrix, where the mt-tRNA and mitochondrial translation machinery are. The matrix location is inferred from the presequence, the function and the Nagao 2009 mitochondrial biogenesis context. I did not verify direct localization experiments.

3. Pathway

GATC acts in mitochondrial tRNA aminoacylation, which feeds mitochondrial translation of the 13 mtDNA-encoded OXPHOS subunits. It has no independent signalling role.

4. Suggested GO-level interpretation

These are my inferences, not verified against the existing GOA rows.
- Molecular function. The best fit is a contribution to glutamyl-tRNA(Gln) amidotransferase activity (GO:0050567) rather than direct catalysis, because GatC is a non-catalytic scaffold subunit. The contributes_to qualifier or a structural-subunit framing is more accurate.
- Complex. The glutamyl-tRNA(Gln) amidotransferase complex, mitochondrial.
- Process. Mitochondrial glutaminyl-tRNA aminoacylation via transamidation (GO:0070681, "glutaminyl-tRNAGln biosynthesis via transamidation"). Mitochondrial translation is downstream and should be treated as indirect.
- Cellular component. Mitochondrion or mitochondrial matrix.
- Terms to avoid. Do not use protein binding. Avoid broad terms such as "mitochondrial respiratory chain complex assembly" or cardiac development. These are downstream consequences of the translation defect.

5. Evidence summary and gaps

Open questions, which would need experiments:
- The structural basis of human GatCAB assembly (no human complex structure was found).
- Whether GATC has any role outside tRNA transamidation.
- The biochemical effect of the specific GATC variants. These could be tested by in vitro Gln-tRNA formation assays with recombinant complexes.

6. Sources

• Nagao A, Suzuki T, Katoh T, Sakaguchi Y, Suzuki T. PNAS 2009, PMID:19805282. Cited via UniProt and not retrieved.
• Friederich MW et al. Nat Commun 2018, PMID:30283131: DOAJ record, DOI link, Cambridge repository.
• NCBI Gene 283459, listed in the search results and not opened.
• dismech COXPD42 page.
• UniProt O43716 header, as given in the task.

Before curation, fetch the full texts for both papers and re-quote them verbatim, since the quotes above are paraphrased from search summaries.

Citations

1. https://doaj.org/article/5e2c03b6081043e5add48aba3812d059
2. https://dismech.monarchinitiative.org/pages/disorders/Combined_oxidative_phosphorylation_deficiency_42.html
3. https://dx.doi.org/10.1038/s41467-018-06250-w
4. https://www.repository.cam.ac.uk/handle/1810/286571?show=full
5. https://www.ncbi.nlm.nih.gov/gene/283459