Characterization of micron-scale protein-depleted plasma membrane domains in phosphatidylserine-deficient yeast cells

Abstract

Membrane phase separation to form micron-scale domains of lipids and proteins occurs in artificial membranes; however, a similar large-scale phase separation has not been reported in the plasma membrane of the living cells. We show here that a stable micron-scale protein-depleted region is generated in the plasma membrane of yeast mutants lacking phosphatidylserine at high temperatures. We named this region the ‘void zone’. Transmembrane proteins and certain peripheral membrane proteins and phospholipids are excluded from the void zone. The void zone is rich in ergosterol, and requires ergosterol and sphingolipids for its formation. Such properties are also found in the cholesterol-enriched domains of phase-separated artificial membranes, but the void zone is a novel membrane domain that requires energy and various cellular functions for its formation. The formation of the void zone indicates that the plasma membrane in living cells has the potential to undergo phase separation with certain lipid compositions. We also found that void zones were frequently in contact with vacuoles, in which a membrane domain was also formed at the contact site.

Exocytic plasma membrane flows remodel endoplasmic reticulum–plasma membrane tethering for septin collar assembly

“…ER-PM tethering is dynamically reorganized by changes in PM lipid composition and posttranslational modification–or Ca 2+ -dependent alteration of lipid-binding affinity of the tethering proteins ( 4 , 6 , 53 ). We revealed that PM-localized proteins, including the oligomerized PM-binding motifs of Ist2, were excluded from the bud sites, indicating that PM binding is crucial for the exclusion of ER-PM tethering proteins.…”

Sigma 1 Receptor, Cholesterol and Endoplasmic Reticulum Contact Sites

“…Liquid-ordered membrane domains were observed for ER-mitochondria, ER-PM, and ER-lipid droplet contact sites ( King et al, 2020 ). Recently, it was observed that in phosphatidylserine-deficient yeast strain, a large sterol-rich ‘void’ zone can be formed on the PM ( Mioka et al, 2022 ). Vacuole-PM MCS is preferentially formed with the void zone, even though it is depleted of integral and peripheric membrane proteins ( Mioka et al, 2022 ).…”

“…Recently, it was observed that in phosphatidylserine-deficient yeast strain, a large sterol-rich ‘void’ zone can be formed on the PM ( Mioka et al, 2022 ). Vacuole-PM MCS is preferentially formed with the void zone, even though it is depleted of integral and peripheric membrane proteins ( Mioka et al, 2022 ). According to the proposed model, it is likely that the unique lipid composition of the ER membrane at the MCS is a direct consequence of unique lipid composition of pre-existing ER microdomains that formed the initial basis for their formation.…”

Membrane Contact Sites in Yeast: Control Hubs of Sphingolipid Homeostasis

“…The loss of ER-PM contacts under certain conditions is also compensated by vacuole-PM contact site formation. It was recently discovered that the PM of living yeast cells forms micron-scale protein-depleted regions termed "void zones" [111]. These domains resemble the artificial, phase-separated regions seen in giant unilamellar vesicles and giant PM vesicles but are in fact maintained by cells in an energy-dependent manner.…”

“…Void zones lack association with the cortical ER but instead form contact sites with the vacuole, possibly to prevent membrane integrity defects at the interface of the phase separation which is prone to high membrane permeability [112]. Because the formation of void zones at the PM depends on sphingolipid synthesis [111], void zone-vacuole contacts may be involved in regulating sphingolipid metabolism or organization of the PM.…”