Biology subjects

Lenhard, S.

Publications and source records attributed to Lenhard, S..

5 recordsLinked to original sources

bioRxiv2026

Presequences of non-imported mitochondrial proteins serve as quality control elements in the cytosol

Most mitochondrial proteins are synthesized in the cytosol as precursor proteins with presequences which serve as targeting signals for the mitochondrial matrix, where they are cleaved by the mitochondrial processing peptidase (MPP). In this study, we comprehensively elucidated the role of the presequence and the mature part of mitochondrial precursors in the cytosol, by use of a cytosol-targeted MPP which prematurely processed mitochondrial precursors. Over time, cytoMPP resulted in mitochondrial depletion. However, the cellular response to cytoMPP was surprisingly different to that observed for other models of mitochondrial import inhibition. Cytosolic maturation rendered many proteins stable in the cytosol, indicating that their mature parts lack ubiquitination signals. Accordingly, cytoMPP did not induce the upregulation of the proteasome, which normally is a hallmark of mitochondrial dysfunction. Instead, cytoMPP elicited a heat shock response and impaired the sequestration of precursors in the cytosol. Our observations demonstrate that mitochondrial presequences are more than just address labels. Rather, they play an important role in quality control and orchestrate the cellular response to defects in mitochondrial protein import.

biochemistry↗

bioRxiv2025

Heterooligomerization drives structural plasticity of eukaryotic peroxiredoxins

Peroxiredoxins are highly conserved thiol peroxidases essential for peroxide detoxification, redox signaling, and chaperone activity. Prx1/AhpC-type peroxiredoxins are found throughout the eukaryotic kingdom, where multiple isoforms frequently coexist within the same cell and even in the same subcellular compartment. Long thought to form exclusively homooligomeric structures, we reveal that heterooligomerization is a conserved and important feature of eukaryotic Prx1/AhpC-type peroxiredoxins. We demonstrate that heterooligomer formation modulates peroxoredoxin oligomeric state and enhances structural stability. In yeast, Tsa1-Tsa2 peroxiredoxin heterodecamers form in response to oxidative stress and incorporated Tsa2 stabilizes the decameric state. Beyond yeast, we show that human PRDX1 and PRDX2, as well as plant and parasitic peroxiredoxins, engage in functional heterooligomerization. These findings challenge the long-held paradigm of peroxiredoxin homooligomerization and reveal a novel mechanism for regulating redox homeostasis. Our study provides new insights into peroxiredoxin structural plasticity with broad implications for redox biology, stress responses, and cellular adaptation.

biochemistry↗

bioRxiv2024

Aneuploidy-induced proteostasis disruption impairsmitochondrial functions and mediates aggregation ofmitochondrial precursor proteins through SQSTM1/p62

Aberrant chromosomal content, or aneuploidy, profoundly affects cellular physiology. Even a gain of a single chromosome disrupts proteostasis due to overexpression of numerous proteins. Consequently, cells accumulate SQSTM1/p62-positive cytosolic bodies and show altered proteasomal and lysosomal activity. To elucidate the p62 interaction network in aneuploid cells, we conducted p62 immunoprecipitation and proximity labeling assays followed by mass spectrometry analysis. Our investigation revealed the enrichment of mitochondrial proteins within the cytosolic p62 interactome and proxitome in aneuploid cells, but not in the proxitome spatially confined to autophagosomes. Immunofluorescence microscopy confirmed increased colocalization of p62 with novel interactors and with mitochondrial proteins in polysomic cells. Moreover, we observed mitochondrial defects characterized by increased perinuclear clustering, reduced oxygen consumption, and reduced mitochondrial DNA abundance in polysomic cells. Furthermore, we demonstrate that polysomic cells exhibit reduced import of mitochondrial proteins and accumulation of mitochondrial precursor proteins in the cytosol. Our data suggest that proteotoxic stress induced by chromosome gains leads to the sequestration of mitochondrial precursor proteins into cytosolic p62-bodies and compromises mitochondrial function.

cell biology↗

bioRxiv2022

The metabolite-controlled ubiquitin conjugase Ubc8 promotes mitochondrial protein import by enhancing assembly of the TOM complex

Mitochondria are essential organelles that play a key role in cellular energy metabolism. Transitions between glycolytic and respiratory conditions induce considerable adaptations of the cellular proteome. These metabolism-dependent changes are particularly pronounced for the protein composition of mitochondria. Here we show that the yeast cytosolic ubiquitin conjugase Ubc8 plays a crucial role in the remodeling process when cells transition from respiratory to fermentative conditions. Ubc8 is a conserved and well-studied component of the catabolite control system that is known to regulate the stability of gluconeogenesis enzymes. Unexpectedly, we found that Ubc8 also promotes the assembly of the translocase of the outer membrane of mitochondria (TOM) and stabilizes its cytosol-exposed receptor subunit Tom22. Ubc8 deficiency results in a compromised protein import into mitochondria and a subsequent accumulation of mitochondrial precursor proteins in the cytosol. Our observations show that Ubc8, which is controlled by the prevailing metabolic conditions, promotes the switch from glucose synthesis to glucose usage in the cytosol and induces the biogenesis of the mitochondrial TOM machinery in order to improve mitochondrial protein import during phases of metabolic transition.

biochemistry↗

bioRxiv2020

The mitochondrial surface receptor Tom70 protects the cytosol against mitoprotein-induced stress

Most mitochondrial proteins are synthesized as precursors in the cytosol and post-translationally transported into mitochondria. The mitochondrial surface protein Tom70 acts at the interface of the cytosol and mitochondria. In vitro import experiments identified Tom70 as targeting receptor, particularly for hydrophobic carriers. Using in vivo methods and high content screens, we revisited the question of Tom70 function and considerably expanded the set of Tom70-dependent mitochondrial proteins. We demonstrate that the crucial activity of Tom70 is its ability to recruit cytosolic chaperones to the outer membrane. Indeed, tethering an unrelated chaperone-binding domain onto the mitochondrial surface complements most of the defects caused by Tom70 deletion. Tom70-mediated chaperone recruitment reduces the proteotoxicity of mitochondrial precursor proteins, in particular of hydrophobic inner membrane proteins. Thus, our work suggests that the predominant function of Tom70 is to tether cytosolic chaperones to the outer mitochondrial membrane, rather than to serve as a mitochondria-specifying targeting receptor.

cell biology↗