TUFM (P49411): human mitochondrial elongation factor Tu

Method note. I did only a few targeted searches. Most mechanistic statements come from the UniProt record and the general literature on EF-Tu, not from papers I read this session. They are marked as such.

1. Identity check

• The symbol TUFM matches the UniProt record: P49411, "Elongation factor Tu, mitochondrial", EC 3.6.5.3, human (UniProt header supplied with the task).
• The family and domains fit. It belongs to the TRAFAC translation-factor GTPase class and has a GTP-binding domain (EF-Tu_GTP-bd) and the EF-Tu domain 2 and domain 3 modules (EFTU_2, EFTu-like_2). These are the same domains as bacterial EF-Tu.
• I found no ambiguity with another gene. TUFM is the nuclear-encoded mitochondrial EF-Tu. It is separate from the cytosolic eEF1A and from bacterial tufA/tufB.

2. Primary molecular function

Reaction (EC 3.6.5.3, protein-synthesis GTPase): GTP + H2O → GDP + phosphate, coupled to delivering aminoacyl-tRNA to the A-site of the mitoribosome.

• Ternary complex. In the GTP-bound state, EF-Tu binds aminoacyl-tRNA (aa-tRNA) and forms the EF-Tu·GTP·aa-tRNA complex.
• Decoding. The complex enters the A-site of the mitoribosome, where codon–anticodon pairing triggers GTP hydrolysis.
• Release. EF-Tu·GDP is released, and the aa-tRNA is accommodated in the peptidyl-transferase center.
• Recycling. The mitochondrial nucleotide-exchange factor TSFM (EF-Ts) regenerates EF-Tu·GTP.
• Source. This is inferred from the canonical bacterial and mitochondrial elongation cycle. See Kummer & Ban 2021, Nat Rev Mol Cell Biol 22:307–325, PMID:33594280 (PubMed). That review covers the architecture and mechanism of the mammalian mitochondrial translation apparatus. The search returned no passage on EF-Tu itself, so the specifics above are not quoted from it.
• Substrate specificity. Mitochondrial EF-Tu works with the 22 mt-tRNAs, which are unusual in structure. It handles mitochondrial Met-tRNA only in the elongation role, since initiation uses a formylated Met-tRNA and the separate factor MTIF2. I recall these properties from the biochemical literature but did not re-verify them.

Suggested GO terms
- MF: translation elongation factor activity (GO:0003746), GTPase activity (GO:0003924), GTP binding (GO:0005525), and aminoacyl-tRNA binding (also mitochondrial tRNA binding).
- BP: mitochondrial translational elongation (GO:0070125).
- Avoid: "protein binding".

3. Localization and pathway

• Compartment. The mitochondrial matrix, where it acts on mitoribosomes (inner-membrane-associated).
• Targeting. The protein is a precursor with an N-terminal mitochondrial targeting sequence (UniProt "Flags: Precursor").
• Pathway. Mitochondrial translation elongation, which makes the 13 mtDNA-encoded OXPHOS subunits. Loss of TUFM therefore affects complexes I, III, IV and V, but not complex II, whose subunits are all nuclear-encoded.
• Upstream/downstream. Aminoacylated mt-tRNAs are supplied by the mitochondrial aminoacyl-tRNA synthetases. After peptide-bond formation, EF-G1 (GFM1) catalyzes translocation, and TSFM recycles EF-Tu.

4. Disease evidence

• COXPD4. Biallelic TUFM mutations cause combined oxidative phosphorylation deficiency 4 (OMIM #610678) (OMIM mirror; LOVD).
• Valente et al. 2007 (Am J Hum Genet). This is the founding report. An infant had homozygous c.1016G>A, p.Arg339Gln, with neonatal lactic acidosis, rapidly progressive encephalopathy, severely decreased mitochondrial protein synthesis, and combined deficiency of the mtDNA-dependent respiratory complexes. The same paper described a GFM1 (EF-G1) case (Helmholtz PhenoDis). I recall the PMID as 17160894, but one search source gave 17160893. Verify this PMID before citing it.
• Further cases. R339Q has been seen in other families. A 2024 case report states that only six patients with biallelic pathogenic TUFM variants had been reported at that time (De Gruyter, J Pediatr Endocrinol Metab).
• Interpretation. The defect is in mtDNA-encoded protein synthesis, which is consistent with TUFM being required for mitochondrial translation elongation. This is human genetic evidence of necessity, not a mechanistic assay of its GTPase activity.

5. Non-canonical roles (secondary)

• NLRX1 complex. Lei et al. 2012, Immunity 36:933–946, PMID:22749352 (PMC3397828). TUFM was identified by mass spectrometry as an NLRX1 partner. It also binds the Atg5–Atg12 complex and Atg16L1. Like NLRX1, it dampens RLR-driven type I interferon signaling and promotes autophagy during viral infection (the search summary describes it in these terms; I did not read the full text).
• Caveat. These findings were made largely in mouse and cell-line systems. I treat them as non-core, moonlighting roles. The core function remains mitochondrial translation elongation.

6. Evidence quality summary

7. Suggested follow-ups

• Confirm the Valente 2007 PMID against PubMed.
• Pull primary biochemistry on bovine and human mt-EF-Tu: GTP/GDP affinity, TSFM exchange, and tRNA binding (Spremulli lab).
• Look at recent mitoribosome cryo-EM structures with EF-Tu·GTP·aa-tRNA in the A-site, to cite structural support.

Sources

• Kummer & Ban 2021, PubMed 33594280
• Lei et al. 2012, PMC3397828
• OMIM #610678 mirror
• LOVD COXPD4
• Helmholtz PhenoDis COXPD4
• J Pediatr Endocrinol Metab 2024 case report

Citations

1. https://pubmed.ncbi.nlm.nih.gov/33594280/
2. https://https.ncbi.nlm.nih.gov/omim/610678
3. https://databases.lovd.nl/shared/diseases/02969
4. https://iegext02.helmholtz-munich.de/phenodis/disease/show/3067
5. https://www.degruyterbrill.com/document/doi/10.1515/jpem-2023-0569
6. https://pmc.ncbi.nlm.nih.gov/articles/PMC3397828