LYRM7

LYRM7 (MZM1L) is a mitochondrial matrix chaperone that operates in the final steps of mitochondrial Complex III (CIII) biogenesis by binding and stabilizing the Rieske Fe-S protein UQCRFS1 prior to its translocation and insertion into the late CIII dimeric assembly intermediate of the inner membrane (PMID:23168492). Re-expression of LYRM7 in patient fibroblasts restores reduced UQCRFS1 levels, directly establishing UQCRFS1 stabilization as its core function in human cells (PMID:28694194). The conserved residue Asp25 is functionally critical: a p.Asp25Asn substitution impairs UQCRFS1 maturation and reduces CIII activity, a defect recapitulated by the equivalent yeast mzm1 allele (PMID:24014394). Loss of LYRM7 function through truncating mutations causes profound CIII deficiency with reduced holocomplex, rescuable by LYRM7 re-expression, defining LYRM7 as a cause of mitochondrial CIII-deficiency disease (PMID:27151179, PMID:26912632). Beyond its assembly role, LYRM7 is a transcriptional target of TNF-α/NF-κB signaling, and its depletion in breast cancer cells reduces respiratory supercomplex assembly, elevates ROS, and promotes invasion and migration (PMID:38104742).

1. 2012 High

   Established that LYRM7 is a dedicated chaperone for the Rieske Fe-S protein, answering how UQCRFS1 is stabilized before its membrane insertion during CIII assembly.

   Evidence Co-immunoprecipitation, cellular fractionation, knockdown/complementation in human cells with yeast Mzm1 homology

   PMID:23168492

   Open questions at the time

   • No structure of the LYRM7-UQCRFS1 complex
   • Mechanism of how LYRM7 hands off UQCRFS1 to the inner membrane intermediate not resolved
2. 2013 High

   Identified Asp25 as a functionally critical residue, linking a specific human missense mutation to defective UQCRFS1 maturation and demonstrating disease relevance.

   Evidence Patient mutation analysis with yeast complementation, oxygen consumption and CIII activity assays

   PMID:24014394

   Open questions at the time

   • Structural basis for why Asp25 is required not defined
   • Whether Asp25 contributes to UQCRFS1 binding specifically unresolved
3. 2015 Medium

   Consolidated LYRM7's chaperone role in human CIII biogenesis and placed it within the broader LYR-motif assembly-factor superfamily.

   Evidence Cell-based complementation and biochemical assays; comparative structural analysis of paralogous LYRMs (LYRM3, LYRM6)

   PMID:25686363 PMID:25914718

   Open questions at the time

   • Structural data are for paralogs, not LYRM7 directly
   • Whether LYRM7 anchors acyl-carrier protein like other LYRMs untested
4. 2016 Medium

   Demonstrated that loss-of-function mutations cause CIII deficiency reversible by re-expression, confirming LYRM7 as causal for the disease phenotype and reducing the CIII holocomplex.

   Evidence Lentiviral complementation of patient fibroblasts, spectrophotometric CIII assays, BN-PAGE, yeast complementation, exome/Sanger sequencing

   PMID:26912632 PMID:27151179

   Open questions at the time

   • Tissue-specific consequences of CIII deficiency not detailed
   • Genotype-phenotype correlation across mutations incomplete
5. 2017 Medium

   Provided direct human-cell evidence that LYRM7 function determines UQCRFS1 protein levels, confirming the stabilization mechanism at the protein level.

   Evidence LYRM7 re-expression in patient fibroblasts with Western blot quantification of UQCRFS1

   PMID:28694194

   Open questions at the time

   • Does not distinguish stabilization from facilitated synthesis/folding kinetics
   • Single patient/cell-line context
6. 2023 Medium

   Extended LYRM7 biology beyond assembly to signaling-regulated mitochondrial control, placing it downstream of TNF-α/NF-κB and linking its loss to supercomplex disruption and a pro-invasive cancer phenotype.

   Evidence TNF-α treatment, NF-κB analysis, siRNA knockdown in MDA-MB-231 cells, BN-PAGE supercomplex assay, ROS measurement, invasion/migration assays, in vivo Infliximab treatment

   PMID:38104742

   Open questions at the time

   • Direct NF-κB binding to the LYRM7 promoter not mapped
   • Causal chain from supercomplex loss to invasion via ROS not fully dissected
   • Single cancer cell-line model

• How LYRM7 structurally engages UQCRFS1 and mechanistically coordinates its release into the membrane-embedded CIII intermediate remains unresolved.
• No experimental structure of LYRM7 or the LYRM7-UQCRFS1 complex
• Handoff mechanism to the late CIII dimeric intermediate undefined
• Regulation of LYRM7 across tissues beyond NF-κB unexplored