Biology subjects

Westermann, B.

Publications and source records attributed to Westermann, B..

4 recordsLinked to original sources

bioRxiv2025

When mitochondria fall apart: Unbalanced mitochondrial segregation triggers loss of mtDNA in the absence of mitochondrial fusion

Mitochondrial biogenesis and inheritance must be carefully regulated alongside cell division to ensure proper mitochondrial function and cell survival. The dynamics of the mitochondrial network, including fusion and fission, play a crucial role in mitochondrial inheritance by facilitating the distribution and quality control of mitochondria. In budding yeast, simultaneous inhibition of both fusion and fission leads to loss of mitochondrial DNA (mtDNA) integrity, resulting in an increased frequency of petite cells. Loss of mitochondrial fusion alone results in the complete loss of mtDNA. While the loss of mtDNA in the absence of mitochondrial fusion has been known for almost 30 years, the reason remained unclear. Here, we investigate the consequences of impaired mitochondrial fusion through depletion of the mitofusin Fzo1. We follow the emerging phenotype by live-cell imaging and the analysis of more than thirty thousand single cells across their cell cycle. Fzo1 depletion causes rapid mitochondrial fragmentation and a reduction in mitochondrial membrane potential, followed by a progressive decline of mtDNA content and cellular growth rate over several cell divisions. During division, Fzo1-depleted daughters obtain an unusually large amount of mitochondria, leaving the mother with too little. This results in a strong disbalance of mitochondrial mass in the population. Additionally, Fzo1-depleted cells lose the ability to adjust mtDNA synthesis to compensate for a low mitochondrial content. The combined effects of unequal distribution and reduced synthesis drive rapid mtDNA loss. These results show how fusion defects lead to mtDNA loss and mitochondrial dysfunction, contributing to understanding diseases linked to fusion defects.

cell biology↗

bioRxiv2022

The intra-mitochondrial contact site formed by Cqd1 and the Por1-Om14 complex modulates architecture and morphology of mitochondria

Mitochondria are essential organelles of eukaryotic cells that are characterized by their unique and complex membrane system. They are confined from the cytosol by an envelope consisting of two membranes. Signals, metabolites, proteins and lipids have to be transferred across these membranes via proteinaceous contact sites to keep mitochondria functional. In the present study we identified a novel mitochondrial contact site that is formed by the inner membrane protein Cqd1 and the outer membrane proteins Por1 and Om14. Similar to the mitochondrial porin, Por1, Cqd1 is highly conserved, suggesting that this complex is conserved in form and function from yeast to human. Cqd1 is a member of the UbiB protein kinase-like family (also called aarF domain containing kinases). It was recently shown that Cqd1 in cooperation with Cqd2 controls the cellular distribution of coenzyme Q by a yet unknown mechanism. Our data suggest that Cqd1 in addition is involved in the homeostasis of phospholipids and contributes to the maintenance of mitochondrial morphology and architecture. Summary statementHere, we show that the conserved mitochondrial inner membrane protein Cqd1 interacts with the outer membrane proteins Por1 and Om14. Additionally, we provide evidence that Cqd1 is important for maintaining mitochondrial homeostasis.

biochemistry↗

bioRxiv2021

Increased levels of the mitochondrial import factor Mia40 prevent the aggregation of polyQ proteins in the cytosol

The formation of protein aggregates is a hallmark of neurodegenerative diseases. Observations on patient material and model systems demonstrated links between aggregate formation and declining mitochondrial functionality, but the causalities remained unclear. We used yeast as model system to analyze the relevance of mitochondrial processes for the behavior of an aggregation-prone polyQ protein derived from human huntingtin. Induction of Q97-GFP rapidly leads to insoluble cytosolic aggregates and cell death. Although this aggregation impairs mitochondrial respiration only slightly, it interferes with efficient import of mitochondrial precursor proteins. Mutants in the import component Mia40 are hypersensitive to Q97-GFP. Even more surprisingly, Mia40 overexpression strongly suppresses the formation of toxic Q97-GFP aggregates both in yeast and in human cells. Based on these observations, we propose that the posttranslational import into mitochondria competes with aggregation-prone cytosolic proteins for chaperones and proteasome capacity. Owing to its rate-limiting role for mitochondrial protein import, Mia40 acts as a regulatory component in this competition. This role of Mia40 as dynamic regulator in mitochondrial biogenesis can apparently be exploited to stabilize cytosolic proteostasis. (174/175 words)

biochemistry↗

bioRxiv2020

A modular two yeast species secretion system for the production and preparative application of fungal peroxygenases

Fungal unspecific peroxygenases (UPOs) are biocatalysts of outstanding interest. Providing access to novel UPOs using a modular secretion system was the central goal of this work. UPOs represent an enzyme class, catalysing versatile oxyfunctionalisation reactions on a broad substrate scope. They are occurring as secreted, glycosylated proteins bearing a haem-thiolate active site and solely rely on hydrogen peroxide as the oxygen source. Fungal peroxygenases are widespread throughout the fungal kingdom and hence a huge variety of UPO gene sequences is available. However, the heterologous production of UPOs in a fast-growing organism suitable for high throughput screening has only succeeded once--enabled by an intensive directed evolution campaign. Here, we developed and applied a modular Golden Gate-based secretion system, allowing the first yeast production of four active UPOs, their one-step purification and application in an enantioselective conversion on a preparative scale. The Golden Gate setup was designed to be broadly applicable and consists of the three module types: i) a signal peptide panel guiding secretion, ii) UPO genes, and iii) protein tags for purification and split-GFP detection. We show that optimal signal peptides could be selected for successful UPO secretion by combinatorial testing of 17 signal peptides for each UPO gene. The modular episomal system is suitable for use in Saccharomyces cerevisiae and was transferred to episomal and chromosomally integrated expression cassettes in Pichia pastoris. Shake flask productions in Pichia pastoris yielded up to 24 mg/L secreted UPO enzyme, which was employed for the preparative scale conversion of a phenethylamine derivative reaching 98.6 % ee. Our results demonstrate a rapid workflow from putative UPO gene to preparative scale enantioselective biotransformations.

synthetic biology↗