Biology subjects

Nunnari, J.

Publications and source records attributed to Nunnari, J..

4 recordsLinked to original sources

bioRxiv2026

ARMC1 regulates mitochondrial fatty acid oxidation through theinsertase/scramblase MTCH2

MTCH2 (mitochondrial carrier homolog 2) is a noncanonical member of the solute carrier family with five transmembrane (TM) helices, localized to the mitochondrial outer membrane. MTCH2's atypical topology creates a membrane-accessible hydrophilic groove, predicted to be necessary for its protein insertase and lipid scramblase activities. MTCH2 is linked to lipid metabolism and obesity and is required for starvation-induced mitochondrial hyperfusion. Here, we show that MTCH2 is a stable component of a complex containing the Armadillo (ARM) repeat-containing protein, ARMC1, and the DnaJ/Hsp40 chaperone protein, DNAJC11. Protein crosslinking, protein structural modeling, and molecular dynamics simulations demonstrate that the ARMC1 alpha-helical C-terminal domain (CTD) inserts into and stably interacts with the MTCH2 hydrophilic groove and blocks its lipid scramblase activity. We observe that starvation-induced mitochondrial fatty acid oxidation (FAO) is negatively regulated by the ARMC1-MTCH2 interaction. In ARMC1-deficient cells, FAO is stimulated compared to wild-type cells and lipid droplet abundance is significantly reduced. The altered lipid phenotype of ARMC1-/- cells is strictly dependent on MTCH2 and is reversed by ARMC1 expression in a manner dependent on its CTD. Beyond this metabolic axis, we also identify a function for ARMC1 in regulating lysosomal distribution and autophagic flux that is independent of its CTD and interaction with MTCH2. Thus, our data support a model in which the MTCH2-ARMC1 interaction functions as a metabolic switch during starvation to regulate the balance between fat storage and fat burning.

cell biology↗

bioRxiv2025

Allosteric Disordering of eIF2B Regulates the Integrated Stress Response

The ternary complex (TC), composed of translation initiation factor eIF2, GTP, and initiator methionyl tRNA, delivers the first amino acid to the ribosome to initiate protein synthesis. The activity of the decameric eukaryotic initiation factor 2B complex (eIF2B) initiates TC assembly by catalyzing GDP to GTP exchange on eIF2, thereby setting the TC levels in the cell. Stress-induced phosphorylation converts eIF2 from the substrate of the GDP/GTP exchange reaction into an inhibitor (eIF2-P) of eIF2B. This conversion reduces the cells TC levels and induces the widespread reprogramming of translation known as the Integrated Stress Response (ISR). Here, we chart an allosteric axis running through eIF2B, revealing the importance of a protrusive -helix in its {beta}-subunit, the latch-helix, that locks onto the -subunit to induce eIF2B activity. eIF2-P binding unhooks the latch-helix, opening eIF2B, which inhibits its GDP/GTP exchange activity. Distinct viral proteins have convergently evolved to bind to eIF2B and stabilize the latch-helix-bound active state. Using these insights, we generated ISR-ACTivating compounds, ISRACTs, that stabilize eIF2B in its inhibited, unlatched state. Our study thus highlights how state-transitions in eIF2B are regulated via long-range allostery.

biochemistry↗

bioRxiv2022

PERK-ATAD3A interaction protects mitochondrial proteins synthesis during ER stress

Widespread repression of protein synthesis rates is a key feature of Endoplasmic Reticulum (ER) stress, mediated by the ER sensor kinase PERK. While select transcripts escape this repression, global translational down-regulation impacts crucial protein levels in all cellular compartments, beyond the ER. How the cell manages this paradox is unclear. PERK has a unique cytoplasmic loop within its kinase domain that binds PERKs target, eIF2. We identified the mitochondrial protein, ATAD3A, as a new interactor of the loop, binding to a highly conserved region within it. During ER stress, increased interaction between ATAD3A and PERK attenuates PERK signalling to eIF2, removing the translational block on several mitochondrial proteins. This occurs at novel context-dependent, mitochondria-ER contact sites. The interaction provides a previously unknown mechanism for fine-tuning translational repression at a local level, mitigating the impact of ER stress on mitochondria. Further, it represents a new target for selective modulation of PERK-eIF2 signalling in diseases from cancer to neurodegeneration. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=153 HEIGHT=200 SRC="FIGDIR/small/501280v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@f74252org.highwire.dtl.DTLVardef@1234633org.highwire.dtl.DTLVardef@d5dc9aorg.highwire.dtl.DTLVardef@8606fe_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2021

Genome-wide CRISPRi screening identifies OCIAD1 as a prohibitin client and regulatory determinant of mitochondrial Complex III assembly in human cells

Dysfunction of the mitochondrial electron transport chain (mETC) is a major cause of human mitochondrial diseases. To identify determinants of mETC function, we screened a genome-wide human CRISPRi library under oxidative metabolic conditions with selective inhibition of mitochondrial Complex III and identified OCIA domain-containing protein 1 (OCIAD1) as a Complex III assembly factor. We find that OCIAD1 is an inner mitochondrial membrane protein that forms a complex with supramolecular prohibitin assemblies. Our data indicate that OCIAD1 is required for maintenance of normal steady state levels of Complex III and the proteolytic processing of the catalytic subunit cytochrome c1 (CYC1). In OCIAD1 depleted mitochondria, unprocessed CYC1 is hemylated and incorporated into Complex III. We propose that OCIAD1 acts as an adaptor within prohibitin assemblies to stabilize and/or chaperone CYC1 and to facilitate its proteolytic processing by the IMMP2L protease.

cell biology↗