Biology subjects

King, M. S.

Publications and source records attributed to King, M. S..

8 recordsLinked to original sources

bioRxiv2026

Tissue-wide metabolic buffering confers resilience to mosaic mitochondrial dysfunction

Mitochondria and oxidative phosphorylation (OxPhos) are essential for cellular homeostasis. However, the phenotypes caused by mitochondrial dysfunction often display remarkable tissue-specificity. What determines the susceptibility of individual cells to metabolic or mitochondrial defects in a complex in vivo tissue context, remains largely unknown. We find that neural stem cells (NSCs) in the developing Drosophila brain can maintain normal proliferation despite severe cell-autonomous OxPhos-dysfunction, provided that sufficient neighbouring cells remain metabolically intact. This tissue-wide buffering progressively fails as the proportion of NSCs with OxPhos dysfunction increases, indicating that the phenotypic threshold for mitochondrial dysfunction is an emergent property of a tissue rather than only of individual cells or cell-types. Mechanistically, we find that OxPhos-deficient NSCs activate a stress-response associated with ATF4/crc-transcriptional activation. NSCs upregulate lactate dehydrogenase (LDH) expression to maintain glycolysis, but their proliferation remains limited by NAD+ regeneration rather than by ATP production. Non-cell-autonomous rescue of NSC-proliferation depends on LDH-dependent NAD+-production in a brain-wide glial network connected by gap junctions and the glutamate/aspartate-transporter Eaat1. These findings demonstrate that the phenotypic threshold for mitochondrial dysfunction is determined by tissue-wide spare metabolic capacity rather than only of individual cells or cell-types. Tissue heterogeneity thus provides resilience to metabolic dysfunction, evidencing key benefits of diversity, and suggesting new therapeutic strategies to enhance endogenous metabolic buffering.

developmental biology↗

bioRxiv2025

Stereospecific GPG acylation by CLN8 drives BMP biosynthesis and its loss leads to Batten disease

Loss-of-function mutations in the endoplasmic reticulum membrane protein CLN8 cause Batten disease, a neurodegenerative lysosomal storage disorder1. Together with the lysosomal enzyme CLN5, CLN8 mediates the biosynthesis of bis(monoacylglycero)phosphate (BMP), a phospholipid essential for lysosomal function and distinguished by its unique S,S stereochemistry2,3. However, the role of CLN8 in BMP synthesis has remained unclear. Here we establish that CLN8 is a glycerophosphoglycerol (GPG) acyltransferase that catalyses the stereospecific acylation of S,S-GPG to produce S,S-lysophosphatidylglycerol (LPG), the CLN5 substrate in BMP synthesis. Using cryo-electron microscopy, we resolve structures of the CLN8 homodimer in apo and substrate-bound states at 2.7 [A] resolution, revealing the active site architecture and a ping-pong acyl transfer mechanism. Batten disease-causing missense mutations impair CLN8 enzymatic activity in vitro and reduce BMP levels in a Cln8R24G knock- in mouse, whereas the Cln8mnd mouse frameshift mutation causes complete loss of BMP in vivo. Exogenous S,S-LPG, but not the R,S stereoisomer, restored BMP synthesis in CLN8- deficient cells and mice, and improved neurological phenotypes in cln8 mutant zebrafish. Together, these findings define the enzymatic function of CLN8, elucidate the biochemical basis of CLN8 Batten disease, and establish a proof-of-concept for treating it through stereospecific BMP precursor supplementation.

biochemistry↗

bioRxiv2023

A mitochondrial carrier transports glycolytic intermediates to link cytosolic and mitochondrial glycolysis in the human gut parasite Blastocystis

Stramenopiles form a clade of diverse eukaryotic organisms, including multicellular algae, the fish and plant pathogenic oomycetes, such as the potato blight Phytophthora, and the human intestinal protozoan Blastocystis. In most eukaryotes, glycolysis is a strictly cytosolic metabolic pathway that converts glucose to pyruvate, resulting in the production of NADH and ATP. In contrast, stramenopiles have a branched glycolysis in which the enzymes of the pay-off phase are located in both the cytosol and the mitochondrial matrix. Here, we identify a mitochondrial carrier in Blastocystis that can transport glycolytic intermediates, such as dihydroxyacetone phosphate and glyceraldehyde-3-phosphate, across the mitochondrial inner membrane, linking the cytosolic and mitochondrial branches of glycolysis. Comparative analyses with the phylogenetically-related human mitochondrial oxoglutarate carrier (SLC25A11) and dicarboxylate carrier (SLC25A10) show that the glycolytic intermediate carrier has lost its ability to transport the canonical substrates malate and oxoglutarate. Blastocystis lacks several key components of oxidative phosphorylation required for the generation of mitochondrial ATP, such as complexes III and IV, ATP synthase and ADP/ATP carriers. The presence of the glycolytic pay-off phase in the mitochondrial matrix generates ATP, which powers energy-requiring processes, such as macromolecular synthesis, as well as NADH, used by mitochondrial complex I to generate a proton motive force to drive the import of proteins and molecules. Given its unique substrate specificity and central role in carbon and energy metabolism, the carrier for glycolytic intermediates identified here represents a specific drug and pesticide target against stramenopile pathogens, which are of great economic importance.

biochemistry↗

bioRxiv2023

Colocalization of Cancer Associated Biomarkers on Single Extracellular Vesicles for Early Cancer Detection

Detection of cancer early, when it is most treatable, remains a significant challenge due to the lack of diagnostic methods sufficiently sensitive to detect nascent tumors. Early-stage tumors are small relative to their tissue of origin, heterogeneous, and infrequently manifest in clinical symptoms. Detection of their presence is made more difficult by a lack of abundant tumor-specific indicators (i.e., protein biomarkers, circulating tumor DNA, etc.) that would enable detection using a non-invasive diagnostic assay. In addition, many benign conditions manifest in a similar manner, thus discriminating an early-stage cancerous lesion from a benign tumor can present additional challenges and result in unnecessary medical procedures. To overcome these obstacles, we have developed a liquid biopsy assay that interrogates circulating extracellular vesicles (EVs) to detect tumor-specific biomarkers colocalized on the surface of individual EVs. Extracellular vesicles from all cell types, including early-stage tumors, are known to be abundant in blood, are remarkably stable, and serve as a biopsy of their cell of origin. The detection of a colocalized combination of cancer associated biomarkers that provide tumor specificity on the surface of extracellular vesicles enables the discrimination of early- and late-stage cancer from non-malignant conditions.

cancer biology↗

bioRxiv2021

Key features of inhibitor binding to the human mitochondrial pyruvate carrier hetero-dimer

The mitochondrial pyruvate carrier (MPC) has emerged as a promising drug target for metabolic disorders, including non-alcoholic steatohepatitis and diabetes, metabolically dependent cancers and neurodegenerative diseases. Human MPC is a protein complex, but the composition of its active form is debated and the mechanisms of transport and inhibition are not resolved. We have recombinantly expressed and purified the human hetero-complex MPC1L/MPC2 and demonstrate that it is a functional hetero-dimer, like the yeast MPC hetero-dimers. Unlike the latter, human MPC1L/MPC2 binds the known inhibitors with high potencies. We identify the essential chemical features shared between these structurally diverse inhibitors and demonstrate that high affinity binding is not attributed to covalent bond formation with MPC cysteines, as previously thought. We also identify 14 new inhibitors of MPC, one outperforming the most potent compound UK5099 by tenfold. Two of them are the commonly prescribed drugs entacapone and nitrofurantoin, suggesting possible off-target mechanisms associated with their adverse effects. This work advances our understanding of MPC inhibition and will accelerate the development of clinically relevant MPC modulators.

molecular biology↗

bioRxiv2020

Structural Insight into Mitochondrial Beta-Barrel Outer Membrane Protein Biogenesis

In mitochondria, {beta}-barrel outer membrane proteins mediate protein import, metabolite transport, lipid transport, and biogenesis. The Sorting and Assembly Machinery (SAM) complex consists of three proteins that assemble as a 1:1:1 complex to fold {beta}-barrel proteins and insert them into the mitochondrial outer membrane. We report cryoEM structures of the SAM complex from Myceliophthora thermophila, which show that Sam50 forms a 16-stranded transmembrane {beta}-barrel with a single polypeptide-transport-associated (POTRA) domain extending into the intermembrane space. Sam35 and Sam37 are located on the cytosolic side of the outer membrane, with Sam35 capping Sam50, and Sam37 interacting extensively with Sam35. Sam35 and Sam37 each adopt a GST-like fold, with no functional, structural, or sequence similarity to their bacterial counterparts. Structural analysis shows how the Sam50 {beta}-barrel opens a lateral gate to accommodate its substrates. The SAM complex structure suggests how it interacts with other mitochondrial outer membrane proteins to create supercomplexes.

biochemistry↗

bioRxiv2018

Screening of candidate substrates and coupling ions of transporters by thermostability shift assays

Substrates of most transport proteins have not been identified, limiting our understanding of their role in physiology and disease. Traditional identification methods use transport assays with radioactive compounds, but they are technically challenging and many compounds are unavailable in radioactive form or are prohibitively expensive, precluding large-scale trials. Here, we present a high-throughput screening method that can identify candidate substrates from libraries of unlabeled compounds. The assay is based on the principle that transport proteins recognize substrates through specific interactions, which lead to enhanced stabilization of the transporter population in thermostability shift assays. Representatives of three different transporter (super)families were tested, which differ in structure as well as transport and ion coupling mechanisms. In each case, the substrates were identified correctly from a large set of chemically related compounds, including stereo-isoforms. In some cases, stabilization by substrate binding was enhanced further by ions, providing testable hypotheses on energy coupling mechanisms.

biophysics↗

bioRxiv2018

Major concerns with the integrity of the mitochondrial ADP/ATP carrier in dodecyl-phosphocholine used for solution NMR studies

Hereby, we wish to note our objections to a paper called \"Substrate-modulated ADP/ATP-transporter dynamics revealed by NMR relaxation dispersion\" by Bruschweiler et al., published in NSMB in 20151. The subject is the yeast mitochondrial ADP/ATP carrier AAC3, which we have studied in great detail ourselves. In particular, we have solved its structure by electron2and x-ray crystallography3 and have studied its interactions with the specific inhibitors atractyloside (ATR) and carboxyatractyloside (CATR) by single-molecule force spectroscopy4. In this paper, the authors claim that AAC3 can be refolded to homogeneity from inclusion bodies produced in Escherichia coli by using the detergent dodecyl-phosphocholine (DPC), better known as Foscholine-12 (Anatrace), and that AAC3 is maintained in a folded and active state for the duration of isothermal titration calor ...

biophysics↗