Biology subjects

Voos, W.

Publications and source records attributed to Voos, W..

4 recordsLinked to original sources

bioRxiv2022

Hsp78-interaction proteome highlights chaperone role during protein aggregation in mitochondria under heat stress

Proteins of the Hsp100 chaperone family support protein homeostasis, the maintenance of protein activity under stress, by refolding aggregated proteins or targeting them for degradation. Hsp78, the ClpB-type mitochondrial member of the Hsp100 family, can be found in lower eukaryotes like yeast. Although Hsp78 has been shown to contribute to protection against elevated temperatures in yeast, the biochemical mechanisms underlying this mitochondria-specific thermotolerance are still largely unclear. To identify endogenous chaperone substrate proteins, we generated an Hsp78-ATPase mutant with a stabilized substrate binding behaviour. We used two SILAC-based quantitative mass spectrometry approaches to analyze the role of Hsp78 during heat stress-induced mitochondrial protein aggregation and disaggregation processes on a proteomic level. In the first setup, Hsp78-interacting polypeptides were identified to reveal the endogenous substrate spectrum of the chaperone. Our analysis revealed that Hsp78 is interacting with a wide variety of proteins related to metabolic functions including energy production and protein synthesis, as well as other chaperones, thus maintaining crucial functions for mitochondrial stress resistance. We compared these interaction data with a second experimental setup that focussed on the on overall aggregation and disaggregation processes in mitochondria under heat stress on a proteomic level. This revealed specific aggregation-prone protein populations and demonstrated the direct quantitative impact of Hsp78 on stress-dependent protein solubility under different conditions. We conclude that Hsp78 together with its cofactors represents a recovery system that protects major mitochondrial metabolic functions during heat stress as well restores protein biogenesis capacity after return to normal conditions.

cell biology↗

bioRxiv2021

Proteomic analysis of the role of the quality control protease LONP1 in mitochondrial protein aggregation

The mitochondrial matrix protease LONP1 is an essential part of the organellar protein quality control system. LONP1 has been shown to be involved in respiration control and apoptosis. Furthermore, a reduction in LONP1 level correlates with ageing processes. Up to now, the effects of a LONP1 defect were mostly studied by utilizing transient, siRNA-mediated knockdown approaches. We generated a new cellular model system for studying the impact of LONP1 on mitochondrial protein homeostasis by a CRISPR/Cas-mediated genetic knockdown (gKD). These cells show a stable reduction of LONP1 along with a mild phenotype characterized by absent morphological differences and only small negative effects on mitochondrial functions under normal culture conditions. To assess the consequences of a permanent LONP1 depletion on the mitochondrial proteome, we analyzed the alterations of protein levels by quantitative mass spectrometry, demonstrating small adaptive changes, in particular concerning mitochondrial protein biogenesis. In an additional proteomic analysis, we determined the temperature-dependent aggregation behavior of mitochondrial proteins and its dependence on a reduction of LONP1 activity, demonstrating the important role of the protease for mitochondrial protein homeostasis in mammalian cells. We identified a significant number of mitochondrial proteins that are affected by LONP1 activity concerning their stress-induced solubility. Taken together, our results suggest a very good applicability of the LONP1 gKD cell line as a model system for human ageing processes.

cell biology↗

bioRxiv2020

Accessing mitochondrial protein import in living cells by protein microinjection

Mitochondrial protein biogenesis relies almost exclusively on the expression of nuclear-encoded polypeptides. The current model postulates that most of these proteins have to be delivered to their final mitochondrial destination after their synthesis in the cytoplasm. However, the knowledge of this process remains limited due to the absence of proper experimental real-time approaches to study mitochondria in their native cellular environment. We developed a gentle microinjection procedure for fluorescent reporter proteins allowing a direct non-invasive study of protein transport in living cells. As a proof of principle, we visualized potential-dependent protein import into mitochondria inside intact cells in real-time. We validated that our approach does not distort mitochondrial morphology and preserves the endogenous expression system as well as mitochondrial protein translocation machinery. We observed that a release of nascent polypeptides chains from actively translating cellular ribosomes by puromycin strongly increased the import rate of the microinjected preprotein. This suggests that a substantial amount of mitochondrial translocase complexes were involved in co-translational protein import of endogenously expressed preproteins. Our protein microinjection method opens new possibilities to study the role of mitochondrial protein import in cell models of various pathological conditions as well as aging processes.

cell biology↗

bioRxiv2018

High aggregation sensitivity of mammalian mitochondrial elongation factor Tu (Tufm) as a sensor for organellar stress

As proteins in mammalian cells exhibit optimal stability at natural temperatures, small temperature variations may cause unfolding and subsequent non-specific aggregation. As this process leads to a loss of function of the affected polypeptides as well as to further cytotoxic stress, aggregate formation has been recognized as a major pathogenic factor in human diseases. In this study we determined the impact of physiological heat stress on mammalian mitochondria on a proteomic level. The overall solubility of endogenous mitochondrial proteins was only marginally affected by a treatment at elevated temperatures. However, we identified a small subset of polypeptides that exhibited an exceptionally high sensitivity to heat stress. The mitochondrial translation elongation factor Tu (Tufm), a protein essential for organellar protein biosynthesis, was highly aggregation-prone and lost its solubility already under mild heat stress conditions. In parallel, mitochondrial translation as well as the import of cytosolic proteins was defective in heat stressed mitochondria. Both types of nascent polypeptides, derived from translation as well as from import exhibited a strong heat-induced aggregation tendency. We propose a model that a quick and specific inactivation of elongation factors may prevent an accumulation of misfolded nascent polypeptides and thereby attenuate proteotoxicity under stress.

cell biology↗