Biology subjects

Schuck, S.

Publications and source records attributed to Schuck, S..

9 recordsLinked to original sources

bioRxiv2026

ESCRT proteins organise stress-induced organelle contact between endoplasmic reticulum and Golgi

ESCRT proteins remodel membranes at many cell organelles, including the endoplasmic reticulum (ER). Here, we investigate whether ESCRTs in budding yeast participate in stress-induced ER reorganisation. We find that ER stress triggers the formation of tubular ER subdomains that recruit various ESCRT proteins. Recruitment of the major ESCRT-III protein Snf7 is mediated by the ESCRT-associated protein Bro1, a homologue of human ALIX, in a manner that is mechanistically distinct from Bro1 function at endosomes. ESCRT-containing ER subdomains are derived from ceramide-rich ER exit sites and form contacts with the Golgi. Furthermore, Bro1 helps to concentrate the tethering and lipid transfer protein Tcb3, a homologue of human extended synaptotagmins, at these organelle contacts and contributes to cellular fitness when lipid metabolism is perturbed. These results indicate that specialised ER exit sites can be repurposed for contacting the Golgi directly and uncover ESCRTs as organisers of stress-inducible ER-Golgi contacts that help maintain cell homeostasis.

cell biology↗

bioRxiv2025

An optimised system for rapid auxin-inducible protein degradation in budding yeast

The auxin system for inducible protein degradation is a powerful tool to investigate protein function. It consists of a degron fused to a target protein, an auxin-related ligand that binds to the degron, and a receptor that recognises the auxin-bound degron and mediates proteasomal degradation of the target protein. Variants of all system components are available, and we here test three degrons, three auxins and three degron receptors to identify optimal combinations of these variants in budding yeast. We show that the degrons mIAA7 or AID* together with adamantyl-auxin and the degron receptor OsTIR1(F74G) allow particularly rapid and extensive degradation. Basal degradation in the absence of auxin is generally low and can be prevented entirely by inducible expression of OsTIR1(F74G). Finally, we demonstrate that the remarkable efficiency of this system makes it competitive with established chemical inhibitors, such as tunicamycin and MG132, and with temperature-sensitive mutant alleles. These findings will aid the effective application of the auxin system.

cell biology↗

bioRxiv2025

Dynamic Organellar Mapping in yeast reveals extensive protein localization changes during ER stress

Sophisticated techniques are available for systematic studies of yeast cell biology. However, it remains challenging to investigate protein subcellular localization changes on a proteome-wide scale. Here, we apply Dynamic Organellar Maps (DOMs) by label-free mass spectrometry to detect localization changes of native, untagged proteins during endoplasmic reticulum (ER) stress. We find that hundreds of proteins shift between cellular compartments. For example, we show that numerous secretory pathway proteins accumulate in the ER, thus defining the extent and selectivity of ER retention of misfolded proteins. Furthermore, we identify candidate cargo proteins of the ER reflux pathway, determine constituents of reticulon clusters that segregate from the remainder of the ER and provide evidence for altered nuclear pore complex composition and nuclear import. These findings uncover protein relocalization as a major aspect of cellular reorganization during ER stress and establish DOMs as a powerful discovery tool in yeast.

cell biology↗

bioRxiv2024

Reprograming of the ubiquitin ligase Ubr1 by intrinsically disordered Roq1 through cooperating multifunctional motifs

One way cells control the speed and specificity of protein degradation is by regulating the activity of ubiquitin ligases. Upon proteotoxic stress in yeast, the intrinsically disordered protein Roq1 binds the ubiquitin ligase Ubr1 as a pseudosubstrate, thereby modulating the degradation of substrates of the N-degron pathway and promoting the elimination of misfolded proteins. The mechanism underlying this reprograming of Ubr1 is unknown. Here, we show that Roq1 controls Ubr1 by means of two cooperating multifunctional motifs. The N-terminal arginine and a short hydrophobic motif of Roq1 interact with Ubr1 as part of a heterobivalent binding mechanism. Via its N-terminal arginine, Roq1 regulates the ubiquitination of various N-degron substrates and folded proteins. Via its hydrophobic motif, Roq1 accelerates the ubiquitination of misfolded proteins. These findings reveal how a small, intrinsically disordered protein with a simple architecture engages parallel channels of communication to reprogram a functionally complex ubiquitin ligase.

biochemistry↗

bioRxiv2020

Phosphorylation of the GARP Subunit Vps53 by Snf1 Leads to the Formation of a Golgi-Mitochondria Contact Site (GoMiCS) in Yeast

The canonical function of the Golgi-associated retrograde protein (GARP) complex is the tethering of transport carriers. GARP belongs to the complexes associated with tethering containing helical rods (CATCHR) family and is a hetero-tetrameric complex consisting of the subunits Vps51, Vps52, Vps53 and Vps54. How the activity of GARP is regulated and if it possesses other functions besides tethering remains largely unknown. Here we identify the GARP subunit Vps53 as a novel regulatory target of the S. cerevisiae AMP kinase (AMPK) homolog Snf1. We find that Vps53 is both an in vivo and in vitro target of Snf1 and show that phosphorylation depends on the nature and quantity of the available carbon source. Phosphorylation of Vps53 does not affect the canonical trafficking pathway, but results in altered mitochondrial dynamics and the formation of a previously unknown contact site between the Golgi apparatus and mitochondria, termed GoMiCS. Our results provide an example of a subunit of a CATCHR complex with a constitutive function in membrane trafficking and an inducible role in organelle contact site formation. We anticipate our results to be the starting point for the characterization of this novel contact site.

cell biology↗

bioRxiv2020

Control of endoplasmic reticulum membrane biogenesis by regulators of lipid metabolism

Cells dynamically adapt organelle size to current physiological demand. Organelle growth requires membrane biogenesis and therefore needs to be coordinated with lipid metabolism. The endoplasmic reticulum (ER) can undergo massive expansion, but the regulatory mechanisms that govern ER membrane biogenesis are largely unclear. Here, we conduct a genetic screen for factors involved in ER membrane expansion in budding yeast and identify the ER transmembrane protein Ice2 as a strong hit. We show that Ice2 promotes ER membrane biogenesis by opposing the phosphatidic acid phosphatase Pah1, which is called lipin in metazoa. Ice2 inhibits the conserved Nem1-Spo7 complex, which dephosphorylates and thus activates Pah1. Furthermore, Ice2 cooperates with the transcriptional regulation of lipid synthesis genes and helps to maintain ER homeostasis during ER stress. These findings establish inhibition of the lipin phosphatase complex as an important mechanism for controlling ER membrane biogenesis.

cell biology↗

bioRxiv2019

ESCRT machinery mediates selective microautophagy of endoplasmic reticulum

ER-phagy, the selective autophagy of endoplasmic reticulum (ER), safeguards organelle homeostasis by eliminating misfolded proteins and regulating ER size. ER-phagy can occur by macroautophagic and microautophagic mechanisms. While dedicated machinery for macro-ER-phagy has been discovered, the molecules and mechanisms mediating micro-ER-phagy remain unknown. Here, we first show that micro-ER-phagy in yeast involves the conversion of stacked cisternal ER into multilamellar ER whorls during microautophagic uptake into lysosomes. Second, we identify the conserved Nem1-Spo7 phosphatase complex and ESCRT proteins as key components for micro-ER-phagy. Third, we demonstrate that macro- and micro-ER-phagy are parallel pathways with distinct molecular requirements. Finally, we provide evidence that ESCRT proteins directly function in scission of the lysosomal membrane to complete the microautophagic uptake of ER. These findings establish a framework for a mechanistic understanding of micro-ER-phagy and, thus, a comprehensive appreciation of the role of autophagy in ER homeostasis.

cell biology↗

bioRxiv2018

Pyrophosphate modulates stress responses via SUMOylation

Pyrophosphate (PPi), a byproduct of macromolecule biosynthesis is maintained at low levels by soluble inorganic pyrophosphatases (sPPase) found in all eukaryotes. In plants, H+-pumping pyrophosphatases (H+-PPase) convert the substantial energy present in PPi into an electrochemical gradient. We show here, that both cold- and heat stress sensitivity of fugu5 mutants lacking the major H+-PPase isoform AVP1 is caused by reduced SUMOylation. In addition, we show that increased PPi concentrations interfere with SUMOylation in yeast and we provide evidence that SUMO activating E1-enzymes are inhibited by micromolar concentrations of PPi in a non-competitive manner. Taken together, our results do not only provide a mechanistic explanation for the beneficial effects of AVP1 overexpression in plants but they also highlight PPi as an important integrator of metabolism and stress tolerance.

biochemistry↗

bioRxiv2018

The proteasome biogenesis regulator Rpn4 cooperates with the unfolded protein response to promote resistance to endoplasmic reticulum stress

Misfolded proteins in the endoplasmic reticulum (ER) activate the unfolded protein response (UPR), which enhances protein folding to restore homeostasis. Additional pathways respond to ER stress, but how they help counteract protein misfolding is incompletely understood. Here, we develop a titratable system for the induction of ER stress in yeast to enable a genetic screen for factors that augment stress resistance independently of the UPR. We identify the proteasome biogenesis regulator Rpn4 and show that it cooperates with the UPR. Rpn4 abundance increases during ER stress, first by a post-transcriptional, then by a transcriptional mechanism. Induction of RPN4 transcription is triggered by cytosolic mislocalization of secretory proteins, is mediated by multiple signaling pathways and accelerates clearance of misfolded proteins from the cytosol. Thus, Rpn4 and the UPR are complementary elements of a modular cross-compartment response to ER stress.

cell biology↗