Biology subjects

Andreasson, C.

Publications and source records attributed to Andreasson, C..

4 recordsLinked to original sources

bioRxiv2023

Genetic inactivation of essential HSF1 reveals an isolated transcriptional stress response selectively induced by protein misfolding

Heat Shock Factor 1 (Hsf1) in yeast drives the basal transcription of key proteostasis factors and its activity is induced as part of the core heat shock response. Exploring Hsf1 specific functions has been challenging due to the essential nature of the HSF1 gene and the extensive overlap of target promoters with environmental stress response (ESR) transcription factors Msn2 and Msn4 (Msn2/4). In this study, we constructed a viable hsf1{Delta} strain by replacing the HSF1 open reading frame with genes that constitutively express Hsp40, Hsp70 and Hsp90 from Hsf1-independent promoters. Phenotypic analysis showed that the hsf1{Delta} strain grow slowly, is sensitive to heat as well as protein misfolding and accumulates protein aggregates. Transcriptome analysis revealed that the transcriptional response to protein misfolding induced by azetidine-2-carboxylic acid is fully dependent of Hsf1. In contrast, the hsf1{Delta} strain responded to heat shock through the ESR. Following HS, Hsf1 and Msn2/4 showed functional compensatory induction with stronger activation of the remaining stress pathway when the other branch was inactivated. Thus, we provide a long overdue genetic test of the function of Hsf1 in yeast using the novel hsf1{Delta} construct. Our data highlight that the accumulation of misfolded proteins is uniquely sensed by Hsf1-Hsp70 chaperone titration inducing a highly selective transcriptional stress response.

molecular biology↗

bioRxiv2023

LDO proteins and Vac8 form a vacuole-lipid droplet contact site required for lipophagy in response to starvation

Lipid droplets (LDs) are fat storage organelles critical for energy and lipid metabolism. Upon nutrient exhaustion, cells consume LDs via gradual lipolysis or via lipophagy, the en bloc uptake of LDs into the vacuole. Here, we show that LDs dock to the vacuolar membrane via a contact site that is required for lipophagy in yeast. The LD-localized LDO proteins carry an intrinsically disordered region that associates with vacuolar Vac8 to form vCLIP, the vacuolar-LD contact site. Nutrient limitation drives vCLIP formation, and its inactivation blocks lipophagy. Vac8 is sufficient to recruit LDs to cellular membranes. We establish a functional link between lipophagy and microautophagy of the nucleus, both requiring Vac8 to form respective contact sites upon metabolic stress. In sum, we unravel the molecular architecture of vCLIP, a contact site required for lipophagy, and find that Vac8 provides a platform for multiple and competing contact sites associated with autophagy.

cell biology↗

bioRxiv2021

HSP70-binding motifs function as protein quality control degrons

Protein quality control (PQC) degrons are short protein segments that target misfolded proteins for proteasomal degradation, and thus protect cells against the accumulation of potentially toxic non-native proteins. Studies have shown that PQC degrons are hydrophobic and rarely contain negatively charged residues, features which are shared with chaperone-binding regions. Here we explore the notion that chaperone-binding regions may function as PQC degrons. When directly tested, we found that a canonical Hsp70-binding motif (the APPY peptide) functioned as a dose-dependent PQC degron both in yeast and in human cells. In yeast, Hsp70, Hsp110, Fes1, and the E3 Ubr1 target the APPY degron. Screening revealed that the sequence space within the chaperone-binding region of APPY that is compatible with degron function is vast. We find that the number of exposed Hsp70-binding sites in the yeast proteome correlates with a reduced protein abundance and half-life. Our results suggest that when protein folding fails, chaperone-binding sites may operate as PQC degrons, and PQC-linked degradation therefore overlaps in specificity with chaperone binding. This sheds new light on how the PQC system has evolved to exploit the intrinsic capacity of chaperones to recognize misfolded proteins, thereby placing them at the nexus of protein folding and degradation. Significance StatementIt is broadly accepted that misfolded proteins are often rapidly degraded by the ubiquitin-proteasome system, but how cells specifically recognize this immensely diverse group of proteins is largely unknown. Here we show that upon uncoupling of protein folding from protein degradation, a canonical chaperone-binding motif doubles as a degradation signal (degron), and that within the context of a Hsp70-binding region, many sequences are compatible with degron function. We find that degradation is correlated with the number of Hsp70-binding sites within a protein, and that the number of exposed Hsp70-binding sites in the yeast proteome correlates with more rapid degradation.

biochemistry↗

bioRxiv2020

Evolutionarily conserved chaperone-mediated proteasomal degradation of a disease-linked aspartoacylase variant

Canavan disease is a severe progressive neurodegenerative disorder that is characterized by swelling and spongy degeneration of brain white matter. The disease is genetically linked to polymorphisms in the aspartoacylase (ASPA) gene, including the substitution C152W. ASPA C152W is associated with greatly reduced protein levels in cells, yet biophysical experiments suggest a wild-type like thermal stability. Here, we examine the stability and degradation pathway of ASPA C152W. When we expressed ASPA C152W in Saccharomyces cerevisiae, we found a decreased steady state compared to wild-type ASPA as a result of increased proteasomal degradation. However, molecular dynamics simulations of ASPA C152W did not substantially deviate from wild-type ASPA, indicating that the native state is structurally preserved. Instead, we suggest that the C152W substitution prevents ASPA from reaching its stable native conformation, presumably by impacting on de novo folding. Systematic mapping of the protein quality control components acting on misfolded and aggregation-prone species of C152W, revealed that the degradation is highly dependent on the molecular chaperone Hsp70, its co-chaperone Hsp110 as well as several quality control E3 ubiquitin-protein ligases, including Ubr1. In human cells, ASPA C152W displayed increased proteasomal turnover that was similarly dependent on Hsp70 and Hsp110. We propose that Hsp110 is a potential therapeutic target for misfolding ASPA variants that trigger Canavan disease due to excessive degradation.

biochemistry↗