Biology subjects

Tokatlidis, K.

Publications and source records attributed to Tokatlidis, K..

4 recordsLinked to original sources

bioRxiv2026

A cotranslational role for selenocysteine in productive protein folding

Selenocysteine (Sec) is generally regarded as the catalytic determinant that distinguishes selenoproteins from their cysteine (Cys)-containing counterparts. Consequently, the biological significance of Sec has largely been attributed to its unique chemical properties within mature proteins. Here, we uncover an unexpected role for Sec in protein biogenesis. Using the endoplasmic reticulum selenoprotein SELENOM as a model, we show that replacement of Sec with Cys redirects the protein into an alternative assembly pathway, resulting in formation of a stable domain-swapped homodimer. Biochemical and structural analyses demonstrate that this phenotype cannot be explained solely by altered active-site chemistry, as dimerisation persists following extensive active-site mutagenesis. Remarkably, reintroduction of Sec at alternative positions suppresses dimer formation, including when Sec is placed within a cleaved signal peptide and is absent from the mature protein. Thus, identical protein sequences can adopt distinct folding outcomes depending on whether Sec incorporation occurred during biosynthesis. These findings reveal a previously unrecognised role for Sec in productive protein folding and raise the possibility that evolutionary retention of the Sec incorporation pathway reflects advantages not only in catalysis but also in protein folding.

cell biology↗

bioRxiv2021

A Thioredoxin reductive mechanism balances the oxidative protein import pathway in the intermembrane space of mitochondria

Mitochondria biogenesis crucially depends on the oxidative folding system in the mitochondrial intermembrane space. The oxidative capacity needs however to be balanced by a reductive pathway for optimal mitochondrial fitness. Here we report that the cytosolic thioredoxin machinery fulfils this critical reductive function by dual localisation in the mitochondrial intermembrane space (IMS) via an unconventional import pathway. We show that the presence of the Thioredoxin system in the IMS mediates a hitherto unknown communication between mitochondria biogenesis and the metabolic state of the cell via the cytosolic pool of NADPH. By a combination of complete in vitro reconstitution with purified components, import assays and protein interaction analysis we find that the IMS-localised thioredoxin machinery critically controls the redox state of Mia40, the key player in the MIA pathway in mitochondria thereby ensuring optimal mitochondria biogenesis. Intriguingly, we find that the IMS thioredoxin system fulfils a previously unknown role in the retrograde release of structurally destabilised proteins into the cytosol and protection against oxidative damage, both of which serve as critical mechanisms of mitochondrial surveillance and quality control.

biochemistry↗

bioRxiv2021

One gene - two proteins: The C-terminus of the prototypical M2 muscarinic receptor localizes to the mitochondria

Muscarinic acetylcholine receptors are prototypical G protein-coupled receptors (GPCRs), members of a large family of seven transmembrane receptors mediating a wide variety of extracellular signals. We show here, in cultured cells and in a murine model, that the carboxyl terminal fragment of the muscarinic M2 receptor, comprising the transmembrane regions 6 and 7 (M2tail), is expressed by virtue of an internal ribosome entry site localized in the third intracellular loop. Single cell imaging and import in isolated yeast mitochondria reveals that M2tail, whose expression is upregulated in cells undergoing integrated stress response, does not follow the normal route to the plasma membrane, but is almost exclusively sorted to the mitochondria inner membrane: here it controls oxygen consumption, cell proliferation and the formation of reactive oxygen species by reducing oxidative phosphorylation. Crispr/Cas9 editing of the key methionine where cap-independent translation begins in human induced pluripotent stem cells, reveals the physiological role of this process in influencing cell proliferation and oxygen consumption at the endogenous level. The expression of the C-terminal domain of a GPCR, capable of regulating mitochondrial function, constitutes a hitherto unknown mechanism notably unrelated to its canonical signalling function as a GPCR at the plasma membrane. This work thus highlights a potential novel mechanism thar cells may use for controlling their metabolism under variable environmental conditions, notably as a negative regulator of cell respiration.

cell biology↗

bioRxiv2018

MiR-195 regulates mitochondrial function by targeting mitofusin-2 in breast cancer cells

Mitochondrial dynamics is a highly dysregulated process in cancer. Apoptosis and mitochondrial fission are two concurrent events wherein increased mitochondrial fragmentation serves as a hallmark of apoptosis. We have shown earlier that miR-195 exerts pro-apoptotic effects in breast cancer cells. Herein, we have demonstrated miR-195 as a modulator of mitochondrial dynamics and function. Imaging experiments upon miR-195 treatment have shown that mitochondria undergo extensive fission. We validated mitofusin2 as a potential target of miR-195. Which may provide a molecular explanation for the respiratory defects induced by miR-195 over-expression in breast cancer cells? Active, but not total, mitochondrial mass, was reduced with increasing levels of miR-195. We have further shown that miR-195 enhances mitochondrial SOD-2 expression but does not affect PINK1 levels in breast cancer cells. Collectively, we have revealed that miR-195 is a modulator of mitochondrial dynamics by targeting MFN2 thereby impairing mitochondrial function. Concomitantly, it enhances the scavenger of reactive oxygen species (SOD-2) to maintain moderate levels of oxidative stress. Our findings suggest a therapeutic potential of miR-195 in both ER-positive as well as ER-negative breast cancer cells.

cancer biology↗