Biology subjects

Guerra, R. M.

Publications and source records attributed to Guerra, R. M..

8 recordsLinked to original sources

bioRxiv2026

Pathogenic variants of the mitochondrial copper chaperones SCO1 and SCO2 reshape their respective interactomes and disrupt cellular phospholipid metabolism

SCO1 and SCO2 are required for copper delivery to COX2, a copper-containing subunit of cytochrome c oxidase (COX), yet how mutations in these genes cause distinct, tissue-specific forms of human disease remains poorly understood. To gain further insight into the molecular underpinnings of this clinical heterogeneity, we used BioID to map the interactomes of four pathogenic SCO variants (SCO1 G132S, SCO1 P174L, SCO1 M294V and SCO2 E140K) and the wild-type proteins. While this approach identified many proteins common to both wild-type neighbourhoods, several potential interacting partners unique to each SCO protein were also observed that were consistent with their known roles in COX assembly. Follow-up analyses revealed that SCO1 interacts with COX16 and that this interaction is stabilized within the membrane by a coiled-coil helix-helix interface, with the soluble C-terminal region of COX16 physically bridging SCO1 and COX2 within a ternary complex to facilitate copper delivery. We further observed that COX16 abundance is relatively low in the brain and its association with SCO1 is most severely impaired by the M294V substitution associated with a fatal encephalopathy. Intriguingly, our BioID analyses also detected significant enrichment in each SCO neighbourhood for biosynthetic enzymes and lipases critical to phospholipid metabolism and found that the affinity for these candidate interactors was uniquely perturbed by various pathogenic variants of SCO1 and SCO2. Collectively, our data emphasize the potential of proximity labelling to further define the molecular roles of disease-causing variants that perturb mitochondrial function and suggest that SCO proteins impinge upon phospholipid metabolism.

molecular biology↗

bioRxiv2025

Fmp30 is a phosphatidylinositol hydrolase that regulates CoQ biosynthesis

Coenzyme Q (CoQ, ubiquinone) is a redox-active isoprene lipid that supports fundamental enzymatic and antioxidant roles in mitochondria and beyond. Despite CoQs importance in organismal health and disease, the mechanisms that regulate its biosynthetic pathway remain elusive. Motivated by this, we mined S. cerevisiae multiomics datasets for genes whose disruptions alter CoQ levels and discovered the gene FMP30 as an unexpected negative regulator of CoQ biosynthesis. Loss of FMP30 results in elevated complex Q protein abundance, increased number and intensity of CoQ domains, and ultimately enhanced CoQ biosynthetic flux. We demonstrate that Fmp30, a member of the metallo-{beta}-lactamase super family, displays phospholipase type D activity toward phosphatidylinositol and phosphoinositides, and that its deletion causes marked elevation of these lipid species in purified mitochondria. Collectively, our work nominates Fmp30 as a novel regulator linking mitochondrial phospholipid metabolism to CoQ biosynthesis.

biochemistry↗

bioRxiv2024

RTN4IP1 is essential for the final stages of mitochondrial complex I assembly and coenzyme Q biosynthesis

A biochemical deficiency of mitochondrial complex I (CI) underlies [~]30% of cases of primary mitochondrial disease, yet the inventory of molecular machinery required for CI assembly remains incomplete. We previously characterised patients with isolated CI deficiency caused by segregating variants in RTN4IP1, encoding a mitochondrial NAD(P)H oxidoreductase. Here, we demonstrate that RTN4IP1 deficiency causes a CI assembly defect in both patient fibroblasts and knockout cells, and report that RTN4IP1 is a bona fide CI assembly factor. Complexome profiling revealed accumulation of unincorporated ND5-module and impaired N-module production. RTN4IP1 patient fibroblasts also exhibited defective coenzyme Q biosynthesis, substantiating this emerging function of RTN4IP1. Thus, our data reveal RTN4IP1 plays an essential role in both the terminal stages of CI assembly and in coenzyme Q metabolism, and that pathogenic RTN4IP1 variants impair both functions in patients with mitochondrial disease.

cell biology↗

bioRxiv2024

BRD4-mediated epigenetic regulation of endoplasmic reticulum-mitochondria contact sites is governed by the mitochondrial complex III

Inter-organellar communication is critical for cellular metabolic homeostasis. One of the most abundant inter-organellar interactions are those at the endoplasmic reticulum and mitochondria contact sites (ERMCS). However, a detailed understanding of the mechanisms governing ERMCS regulation and their roles in cellular metabolism are limited by a lack of tools that permit temporal induction and reversal. Through unbiased screening approaches, we identified fedratinib, an FDA-approved drug, that dramatically increases ERMCS abundance by inhibiting the epigenetic modifier BRD4. Fedratinib rapidly and reversibly modulates mitochondrial and ER morphology and alters metabolic homeostasis. Moreover, ERMCS modulation depends on mitochondria electron transport chain complex III function. Comparison of fedratinib activity to other reported inducers of ERMCS revealed common mechanisms of induction and function, providing clarity and union to a growing body of experimental observations. In total, our results uncovered a novel epigenetic signaling pathway and an endogenous metabolic regulator that connects ERMCS and cellular metabolism.

cell biology↗

bioRxiv2023

COQ4 is required for the oxidative decarboxylation of the C1 carbon of Coenzyme Q in eukaryotic cells

Coenzyme Q (CoQ) is a redox lipid that fulfills critical functions in cellular bioenergetics and homeostasis. CoQ is synthesized by a multi-step pathway that involves several COQ proteins. Two steps of the eukaryotic pathway, the decarboxylation and hydroxylation of position C1, have remained uncharacterized. Here, we provide evidence that these two reactions occur in a single oxidative decarboxylation step catalyzed by COQ4. We demonstrate that COQ4 complements an Escherichia coli strain deficient for C1 decarboxylation and hydroxylation and that COQ4 displays oxidative decarboxylation activity in the non-CoQ producer Corynebacterium glutamicum. Overall, our results substantiate that COQ4 contributes to CoQ biosynthesis, not only via its previously proposed structural role, but also via oxidative decarboxylation of CoQ precursors. These findings fill a major gap in the knowledge of eukaryotic CoQ biosynthesis, and shed new light on the pathophysiology of human primary CoQ deficiency due to COQ4 mutations.

biochemistry↗

bioRxiv2023

Hem25p is a mitochondrial IPP transporter

Coenzyme Q (CoQ, ubiquinone) is an essential cellular cofactor comprised of a redox-active quinone head group and a long hydrophobic polyisoprene tail. How mitochondria access cytosolic isoprenoids for CoQ biosynthesis is a longstanding mystery. Here, via a combination of genetic screening, metabolic tracing, and targeted uptake assays, we reveal that Hem25p--a mitochondrial glycine transporter required for heme biosynthesis--doubles as an isopentenyl pyrophosphate (IPP) transporter in Saccharomyces cerevisiae. Mitochondria lacking Hem25p fail to efficiently incorporate IPP into early CoQ precursors, leading to loss of CoQ and turnover of CoQ biosynthetic proteins. Expression of Hem25p in Escherichia coli enables robust IPP uptake demonstrating that Hem25p is sufficient for IPP transport. Collectively, our work reveals that Hem25p drives the bulk of mitochondrial isoprenoid transport for CoQ biosynthesis in yeast.

biochemistry↗

bioRxiv2022

Aim18p and Aim46p are CHI-domain-containing mitochondrial hemoproteins in Saccharomyces cerevisiae.

Chalcone isomerases (CHIs) have well-established roles in the biosynthesis of plant flavonoid metabolites. Saccharomyces cerevisiae possesses two predicted CHI-like proteins, Aim18p (encoded by YHR198C) and Aim46p (YHR199C), but it lacks other enzymes of the flavonoid pathway, suggesting that Aim18p and Aim46p employ the CHI fold for distinct purposes. Here, we demonstrate that Aim18p and Aim46p reside on the mitochondrial inner membrane and adopt CHI folds, but they lack select active site residues and possess an extra fungal-specific loop. Consistent with these differences, Aim18p and Aim46p lack chalcone isomerase activity and also the fatty acid-binding capabilities of other CHI-like proteins, but instead bind heme. We further show that diverse fungal homologs also bind heme and that Aim18p and Aim46p possess structural homology to a bacterial hemoprotein. Collectively, our work reveals a distinct function and cellular localization for two CHI-like proteins, introduces a new variation of a hemoprotein fold, and suggests that ancestral CHI-like proteins were hemoproteins.

biochemistry↗

bioRxiv2021

Structure and functionality of a multimeric human COQ7:COQ9 complex

Coenzyme Q (CoQ, ubiquinone) is a redox-active lipid essential for core metabolic pathways and antioxidant defense. CoQ is synthesized upon the mitochondrial inner membrane by an ill-defined complex Q metabolon. Here we present a structure and functional analyses of a substrate- and NADH-bound oligomeric complex comprised of two complex Q subunits: the hydroxylase COQ7, which performs the penultimate step in CoQ biosynthesis, and the prenyl lipid-binding protein COQ9. We reveal that COQ7 adopts a modified ferritin-like fold with an extended hydrophobic access channel whose substrate binding capacity is enhanced by COQ9. Using molecular dynamics simulations, we further show that two COQ7:COQ9 heterodimers form a curved tetramer that deforms the membrane, potentially opening a pathway for CoQ intermediates to translocate from within the bilayer to the proteins lipid-binding sites. Two such tetramers assemble into a soluble octamer, closed like a capsid, with lipids captured within. Together, these observations indicate that COQ7 and COQ9 cooperate to access hydrophobic precursors and coordinate subsequent synthesis steps toward producing mature CoQ.

biochemistry↗