CRLS1

CRLS1 is the cardiolipin synthase that catalyzes the terminal, committed step of mitochondrial cardiolipin biosynthesis, condensing phosphatidylglycerol with CDP-diacylglycerol at the mitochondrial inner membrane; this activity was established for the yeast ortholog CLS1, whose disruption abolished cardiolipin synthase activity, eliminated detectable cardiolipin, and elevated phosphatidylglycerol ~5-fold (PMID:9614098). The human enzyme is bifunctional, carrying an additional acyl-CoA-dependent lysophosphatidylglycerol acyltransferase activity that remodels phosphatidylglycerol with defined acyl-chain selectivity (C18:1 > C18:2 > C18:0 > C16:0), coupling PG remodeling to cardiolipin production (PMID:20025994). Loss of CRLS1 function depletes cardiolipin, shifts cardiolipin acyl-chain composition, and accumulates the PG substrate, in turn disrupting mitochondrial cristae structure, OXPHOS complex stability and mitochondrial biogenesis, and triggering ER and mitochondrial stress responses (PMID:35147173, PMID:38556544). Biallelic loss-of-function variants in CRLS1 cause a human cardiolipin deficiency disorder, demonstrated in patient-derived fibroblasts with reduced cardiolipin and impaired mitochondrial morphology (PMID:35147173). Functionally, CRLS1-dependent mitochondrial quality control is required for skeletal muscle myogenesis and regeneration (PMID:38556544), and CRLS1 activity is positioned within mitochondrial phospholipid homeostasis such that cardiolipin synthesis contributes to lipid-overload-driven apoptosis when phospholipid efflux is blocked [PMID:bio_10.1101_2025.09.30.679455].

1. 1998 High

   Established the core catalytic identity of the gene: that CLS1/CRLS1 performs the final condensation step of cardiolipin synthesis at the mitochondrial inner membrane, resolving where cardiolipin is made and by what reaction.

   Evidence Gene disruption and heterologous overexpression in yeast and baculovirus-infected insect cells with enzymatic activity and lipid analysis

   PMID:9614098

   Open questions at the time

   • Characterized in yeast ortholog; human enzyme kinetics and structure not addressed
   • No structural model of the active site or membrane topology
2. 2009 High

   Revealed that the human enzyme is bifunctional, adding an acyl-CoA-dependent LPG acyltransferase activity, which connected PG remodeling to cardiolipin production rather than treating CRLS1 as a single-reaction synthase.

   Evidence Purified recombinant hCLS1 in vitro acyltransferase assays with acyl selectivity profiling and overexpression lipid profiling in COS-7 cells

   PMID:20025994

   Open questions at the time

   • Physiological contribution of the LPG acyltransferase activity in vivo not established
   • No structural basis for dual catalysis
3. 2022 High

   Tied CRLS1 directly to human disease, showing biallelic loss-of-function causes cardiolipin deficiency with accumulated PG substrate and mitochondrial dysfunction, converting the enzymatic role into a defined Mendelian disorder.

   Evidence Patient-derived fibroblast lipidomics and proteomics, mouse Crls1 knockout cell lines, and mitochondrial morphology imaging

   PMID:35147173

   Open questions at the time

   • Tissue-specific disease mechanisms not dissected
   • Link between ER/mitochondrial stress response and clinical phenotype unresolved
4. 2024 High

   Demonstrated a physiological requirement for CRLS1 in skeletal muscle, showing its activity maintains mitochondrial quality and is needed for myogenic regeneration in vivo.

   Evidence shRNA knockdown and AAV9-mediated knockdown/overexpression in mice, cristae electron microscopy, OXPHOS complex assays, and cardiotoxin-injury regeneration model

   PMID:38556544

   Open questions at the time

   • Mechanism linking cardiolipin to satellite-cell/myoblast function not resolved
   • Age-dependent decline mechanism not detailed
5. 2025 Medium

   Placed CRLS1 within a broader mitochondrial phospholipid homeostasis network, showing its depletion blocks apoptosis driven by impaired phospholipid efflux, implicating cardiolipin synthesis in pathological lipid-overload death.

   Evidence Genetic epistasis with CRLS1 depletion in BLTP1-deficient cells, apoptosis readout, and lipid profiling (preprint)

   PMID:bio_10.1101_2025.09.30.679455

   Open questions at the time

   • Preprint, not peer-reviewed
   • Direct biochemical link between CRLS1-made cardiolipin and the apoptotic trigger not mechanistically dissected
6. 2026 Medium

   Implicated CRLS1 upregulation as a protective node in ischemic neurons receiving mitochondrial EVs, linking its activity to membrane integrity, respiratory chain stability, and suppression of pyroptosis.

   Evidence hUCMSC mitochondrial EV transfer to neurons with CRLS1 expression, membrane potential, respiratory complex, ROS, and pyroptosis readouts

   PMID:41795421

   Open questions at the time

   • Causal role of CRLS1 not isolated by direct knockdown/rescue in this system
   • Mechanism of CRLS1 upregulation upon EV transfer unknown

• How CRLS1 coordinates its two enzymatic activities, what governs its acyl-chain selectivity in vivo, and how its loss is sensed to drive ER/mitochondrial stress and tissue-specific phenotypes remain unresolved.
• No structural model of the catalytic mechanism or membrane topology
• Regulation of CRLS1 expression/activity across tissues and aging not defined
• Mechanistic coupling between cardiolipin loss and downstream stress/apoptosis pathways incomplete