Trauschke, V. | bioRxiv Science

bioRxiv2022

mtHsp70 converts mitochondrial proteostasis distress into impaired protein import

Functional mitochondria are essential for cell viability and depend on protein import from the cytosol. Impaired protein import initiates various well-characterized cellular programs that rescue or remove dysfunctional mitochondria. However, the molecular mechanism that underlies the initial reduction of protein import into defective mitochondria remained unknown. Here, we found that the redistribution of mtHsp70, mitochondrial chaperone that is involved in both protein import and protein folding, regulates the efficiency of protein import. During early mitochondrial stress, before rescue programs are initiated and membrane potential is affected, mtHsp70-dependent import was specifically impaired and association of mtHsp70 with the import complex reduced. Even under non-stress conditions, the majority of mtHsp70 is found in a substrate-bound state. We propose that the availability of free mtHsp70 limits protein import into mitochondria during stress.

biochemistry↗

bioRxiv2018

On the impact of competing intra- and intermolecular triplet-state quenching on photobleaching and photoswitching kinetics of organic fluorophores

While buffer cocktails remain the gold-standard for photostabilization and photoswitching of fluorescent markers, intramolecular triplet-state quenchers emerge as an alternative strategy to impart fluorophores with self-healing or even functional properties such as photoswitching. In this contribution, we evaluated various combinations of both approaches and show that inter- and intramolecular triplet-state quenching processes compete with each other rather than being additive or even synergistic. Often intramolecular processes dominate the photophysical situation for combinations of covalently-linked and solution-based photostabilizers and photoswitching agents. In this context we identified a new function of intramolecular photostabilizers, i.e., protection of fluorophores from reversible off-switching events caused by solution-additives, which were previously misinterpreted as photobleaching. Our studies also provide practical guidance for usage of photostabilizer-dye conjugates for STORM-type super-resolution microscopy permitting the exploitation of their improved photophysics for increased spatio-temporal resolution. Finally, we provide evidence that the biochemical environment, e.g., proximity of aromatic amino-acids such as tryptophan, reduces the photostabilization efficiency of commonly used buffer cocktails. Not only have our results important implications for a deeper mechanistic understanding of self-healing dyes, but they will provide a general framework to select label positions for optimal and reproducible photostability or photoswitching kinetics.

biophysics↗