Biology subjects

Mioka, T.

Publications and source records attributed to Mioka, T..

4 recordsLinked to original sources

bioRxiv2025

Csf1, a tunnel-like lipid-transfer protein, mediates lipid remodeling and underpins eukaryotic membrane resilience to high hydrostatic pressure and cold

Biological membranes continuously remodel their lipid composition to preserve functionality under environmental stress, yet the molecular basis of this process in eukaryotes remains incompletely understood. Here, we identify the tunnel-like lipid transfer protein Csf1 as a central factor mediating adaptive lipid remodeling that enables Saccharomyces cerevisiae to tolerate high hydrostatic pressure and low temperature. Quantitative lipidomic and membrane biophysical analyses revealed that loss of Csf1 markedly reduces the unsaturation of phosphatidylserine (PS) and phosphatidylethanolamine (PE), leading to rigidification of the endoplasmic reticulum (ER) membrane. Whereas OLE1 overexpression partially mitigated this defect at low temperature, no compensatory response occurred under pressure. Overexpression of the PS/phosphatidylinositol 4-phosphate exchanger Osh6/7 restored PS and PE unsaturation and rescued growth of the Csf1-deficient mutant, indicating a cooperative role in sustaining PS flux at ER-plasma membrane (PM) contact sites. Pressure-induced degradation of the amino-acid permease Bap2 further linked lipid imbalance to membrane-protein instability. By supplying unsaturated PS and PE, Csf1 preserves ER and PM flexibility, defining a conserved mechanism of eukaryotic membrane adaptation to extreme physical stress.

cell biology↗

bioRxiv2022

Wsc1 acts as a piezosensor in Saccharomyces cerevisiae, enhancing glycerol efflux via aquaglyceroporin Fps1 in response to high hydrostatic pressure

The fungal cell wall is the initial barrier for the fungi against diverse external stresses, such as osmolarity changes, harmful drugs, and mechanical injuries. This study explores the roles of osmoregulation and the cell wall integrity (CWI) pathway in response to high hydrostatic pressure in the yeast Saccharomyces cerevisiae. We demonstrate the roles of the transmembrane mechanosensor Wsc1 and aquaglyceroporin Fps1 in a general mechanism to maintain cell growth under high-pressure regimes. The promotion of water influx into cells at 25 MPa, as evident by an increase in cell volume and a loss of the plasma membrane eisosome structure, promotes the activation of Wsc1, an activator of the CWI pathway. The downstream mitogen-activated protein kinase Slt2 was hyperphosphorylated at 25 MPa. Glycerol efflux increases via Fps1 phosphorylation, which is initiated by downstream components of the CWI pathway and contributes to the reduction in intracellular osmolarity under high pressure. The elucidation of the mechanisms underlying adaption to high pressure through the well-established CWI pathway could potentially translate to mammalian cells and provide novel insights into cellular mechanosensation.

cell biology↗

bioRxiv2020

Phospholipid flippases and Sfk1 are essential for the retention of ergosterol in the plasma membrane

Sterols are important lipid components of the plasma membrane (PM) in eukaryotic cells, but it is unknown how the PM retains sterols at a high concentration. Phospholipids are asymmetrically distributed in the PM, and phospholipid flippases play an important role in generating this phospholipid asymmetry. Here, we provide evidence that phospholipid flippases are essential for retaining ergosterol in the PM of yeast. A mutant in three flippases, Dnf1-Lem3, Dnf2-Lem3, and Dnf3-Crf1, and a membrane protein, Sfk1, showed a severe growth defect. We recently identified Sfk1 as a PM protein involved in phospholipid asymmetry. The PM of this mutant showed high permeability and low density, and many nutrient transporters failed to localize to the PM. Staining with the sterol probe filipin and the expression of a sterol biosensor revealed that ergosterol was not retained in the PM. Instead, ergosterol accumulated in an esterified form in lipid droplets. We propose that ergosterol is retained in the PM by the asymmetrical distribution of phospholipids and the action of Sfk1. Once phospholipid asymmetry is severely disrupted, sterols might be exposed on the cytoplasmic leaflet of the PM and actively transported to the endoplasmic reticulum by sterol transfer proteins.

cell biology↗

bioRxiv2020

Phosphatidylserine prevents the generation of a protein-free giant plasma membrane domain in yeast

Membrane phase separation accompanied with micron-scale domains of lipids and proteins occurs in artificial membranes; however, a similar large phase separation has not been reported in the plasma membrane of the living cells. We demonstrate here that a stable micron-scale protein-free region is generated in the plasma membrane of the yeast mutants lacking phosphatidylserine. We named this region the "void zone". Transmembrane proteins, peripheral membrane proteins, and certain phospholipids are excluded from the void zone. The void zone is rich in ergosterol and requires ergosterol and sphingolipids for its formation. These characteristics of the void zone are similar to the properties of the cholesterol-enriched domain in phase-separated artificial membranes. We propose that phosphatidylserine prevents the formation of the void zone by preferentially interacting with ergosterol. We also found that void zones were frequently in contact with vacuoles, in which a membrane domain was also formed at the contact site. Summary statementYeast cells lacking phosphatidylserine generate protein-free plasma membrane domains, and vacuoles contact with this domain. This is the first report of micron-scale plasma membrane domains in living cells.

cell biology↗