Biology subjects

Muellner-Wong, L.

Publications and source records attributed to Muellner-Wong, L..

5 recordsLinked to original sources

bioRxiv2026

MitoSAM-dependent lipoylation controls postnatal heart development via metabolic remodeling

The neonatal heart undergoes a rapid metabolic transition from fetal glycolysis to oxidative phosphorylation, requiring coordinated metabolic remodeling. Mechanisms driving this transition remain unclear. Here, we demonstrate that sufficient mitochondrial S-adenosylmethionine (mitoSAM), imported via the solute carrier Slc25a26, is essential for this shift by sustaining the lipoylation of 2-oxoacid dehydrogenases, critical for TCA cycle activation. Proteomic and metabolomic profiling revealed that reduced mitoSAM availability impaired lipoylation, blocking TCA cycle function and restricting nucleotide synthesis, while mitochondrial gene expression and respiratory capacity remained largely intact. In vivo EdU labeling showed persistent cardiomyocyte proliferation imposing further strain on nucleotide pools. Supplementation with medium-chain triglycerides during the suckling-to-weaning transition restored metabolic function and normalized cardiac growth and morphology. Our data reveal a critical developmental window in which mitoSAM-dependent lipoylation ensures heart maturation.

biochemistry↗

bioRxiv2026

Doxycycline inhibits both apicoplast and mitochondrial translation in apicomplexan parasites

Doxycycline is a tetracycline-class antibiotic used for malarial prophylaxis and as an occasional partner drug in malaria treatment. Doxycyclines antimalarial mechanism of action is attributed to inhibiting the prokaryotic 70S ribosomes of the apicoplast, a non-photosynthetic plastid present in most apicomplexan species including Plasmodium and Toxoplasma. At lower concentrations (<5 M) doxycycline exhibits a delayed death phenotype, typical of inhibitors of apicoplast housekeeping processes. Unlike other delayed death drugs (e.g. clindamycin), doxycycline has rapid schizonticidal activity at higher concentrations (>10 M) via an unknown and apicoplast-independent mechanism. In other eukaryotes, and plausibly in Plasmodium and Toxoplasma, doxycycline inhibits mitochondrial 70S ribosomes. Here we use a mass spectrometry approach to assess steady state and turnover for apicoplast DNA encoded proteins in Plasmodium falciparum. We directly show that these proteins decrease in both abundance and synthesis following treatment with doxycycline and clindamycin. High concentrations of doxycycline, but not clindamycin, also reduced the abundance of a mitochondrial-encoded protein. Proteins encoded by the mitochondrial genome are required for the formation of complexes III and IV in the electron transport chain. We show a reduction in abundance and activity of complex IV following doxycycline treatment in Toxoplasma gondii. High doxycycline concentrations also disrupt oxidative phosphorylation in both P. falciparum and T. gondii, likely as a consequence of impaired complex III and IV formation. For the first time we directly measure apicoplast translation inhibition and characterise doxycycline as a mitochondrial translation inhibitor of P. falciparum and T. gondii.

microbiology↗

bioRxiv2021

Mitochondrial COA7 is a heme-binding protein involved in the early stages of complex IV assembly.

Cytochrome c oxidase assembly factor 7 (COA7) is a metazoan-specific assembly factor, critical for the biogenesis of mitochondrial complex IV (cytochrome c oxidase). Although mutations in COA7 have been linked in patients to complex IV assembly defects and neurological conditions such as peripheral neuropathy, ataxia and leukoencephalopathy, the precise role COA7 plays in the biogenesis of complex IV is not known. Here we show that the absence of COA7 leads to arrest of the complex IV assembly pathway at the initial step where the COX1 module is built, which requires incorporation of copper and heme cofactors. In solution, purified COA7 binds heme with micromolar affinity, through axial ligation to the central iron atom by histidine and methionine residues. Surprisingly, the crystal structure of COA7, determined to 2.4 [A] resolution, reveals a banana-shaped molecule composed of five helix-turn-helix (/) repeats, tethered by disulfide bonds, with a structure entirely distinct from proteins with characterized heme binding activities. We therefore propose a role for COA7 in heme binding/chaperoning in the mitochondrial intermembrane space, this activity being crucial for and providing a missing link in complex IV biogenesis. Significance StatementAssembly factors play key roles in the biogenesis of many mitochondrial protein complexes regulating their stability, activity and incorporation of essential cofactors. COA7 is a metazoan-specific assembly factor, the absence or mutation of which in humans accompanies complex IV assembly defects and neurological conditions. Here we report the crystal structure of COA7 to 2.4 [A] resolution, revealing a banana-shaped molecule composed of five helix-turn-helix (/) repeats, tethered by disulfide bonds. Characterization of pathogenic variants reveals significantly lower stabilities, correlating with the associated disease outcomes. Fascinatingly, COA7 binds heme with micromolar affinity, despite the fact that the protein structure does not resemble previously characterized heme-binding proteins. This provides a possible missing link for heme handling in the mitochondrial intermembrane space.

biochemistry↗

bioRxiv2020

Optic Atrophy-associated TMEM126A is an assembly factor for the ND4-module of Mitochondrial Complex I

Mitochondrial disease is a debilitating condition with a diverse genetic aetiology. Here, we report that TMEM126A, a protein that is mutated in patients with autosomal recessive optic atrophy, participates directly in the assembly of mitochondrial complex I. Using a combination of genome editing, interaction studies and quantitative proteomics, we find that loss of TMEM126A results in an isolated complex I deficiency and that TMEM126A interacts with a number of complex I subunits and assembly factors. Pulse-labelling interaction studies reveal that TMEM126A associates with the newly synthesised mtDNA-encoded ND4 subunit of complex I. Our findings indicate that TMEM126A is involved in the assembly of the ND4 distal membrane module of complex I. Importantly, we clarify that the function of TMEM126A is distinct from its paralogue TMEM126B, which acts in assembly of the ND2-module of complex I, helping to explain the differences in disease aetiology observed between these two genes.

biochemistry↗

bioRxiv2019

Dissecting the Roles of Mitochondrial Complex I Intermediate Assembly (MCIA) Complex Factors in the Biogenesis of Complex I

Mitochondrial Complex I harbors 7 mitochondrial and 38 nuclear-encoded subunits. Its biogenesis requires the assembly and integration of distinct intermediate modules, mediated by numerous assembly factors. The Mitochondrial Complex I Intermediate Assembly (MCIA) complex, containing assembly factors NDUFAF1, ECSIT, ACAD9, and TMEM126B, is required for building the intermediate ND2-module. The role of the MCIA complex and the involvement of other proteins in the biogenesis of this module is unclear. Cell knockout studies reveal that while each MCIA component is critical for complex I assembly, a hierarchy of stability exists centred on ACAD9. We also identify TMEM186 and COA1 as bona fide components of the MCIA complex with loss of either resulting in in MCIA complex defects and reduced complex I assembly. TMEM186 enriches with newly translated ND3, while COA1 enriches with ND2. Our findings provide new functional insights into the essential nature of the MCIA complex in complex I assembly.

biochemistry↗