The lipid raft marker flotillin FloA drives relocalization of the plasma membrane H⁺-ATPase PmaA as a protective response to calcium stress
- 1Department of Molecular and Applied Microbiology, Leibniz Institute for Natural Product Research and Infection Biology - Hans Knöll Institute (Leibniz-HKI), Jena, Germany
- 2Institute for Microbiology, Friedrich Schiller University Jena, Jena, Germany
- 3Cluster of Excellence Balance of the Microverse, Friedrich Schiller University Jena, Jena Germany
Abstract
Biological membranes are laterally heterogeneous and contain specialized microdomains called lipid rafts. Lipid rafts serve as organizational platforms that cluster signaling molecules or modulate membrane protein conformation through their unique lipid environment. There are specific lipid raft marker proteins whose functions remain obscure. One of these proteins is flotillin which has been linked to endocytosis. Here, we investigated the regulation and function of FloA, the sole flotillin homolog in the model fungus Aspergillus nidulans. FloA expression is specifically upregulated in response to calcium stress, which is a regulatory pattern also conserved in Aspergillus fumigatus. BioID proximity labeling revealed that A. nidulans FloA physically interacts with proteins in the endocytic pathway as well as another lipid raft marker, the plasma membrane H+-ATPase PmaA. Under calcium stress, PmaA undergoes internalization from the cytoplasmic membrane. However, when floA is deleted, PmaA internalization is prevented, resulting in cell death. This phenotype of the ΔfloA strain could be mimicked by treating the cells with an endocytosis inhibitor during calcium stress. Together, we demonstrate that FloA is essential for the internalization of PmaA during calcium stress, a process that prevents intracellular calcium overload and promotes cell viability. Our results also provide further evidence for flotillin-assisted endocytosis. Author summary: Lipids and proteins in a cell membrane can cluster together in small regions often called “lipid rafts”, which help the cell interact with its surroundings. Lipid rafts can bring receptors together or influence how membrane proteins behave. Flotillin is a protein often found within lipid rafts, but its exact role is not well understood. Instead of using complex mammalian systems, we studied flotillins in the fungus Aspergillus nidulans, which is a simpler model organism that allows for a better understanding of cellular processes. We found that more flotillins are produced when the fungus is exposed to calcium stress. When flotillins were missing, the cells were unable to remove the protein PmaA from the cell membrane during calcium stress. As a result, the fungus could not cope with the calcium stress and eventually died. Therefore, we propose that flotillins are important for the fungus to reorganize its membranes and coping with calcium stress.
Related
- Combining membrane potential and calcium imaging in brain slices using the voltage-sensitive dye ElectroFluor630 and the calcium indicator Calbryte520
- The kinase homology and dimerization domains in retinal membrane guanylyl cyclase 1 form the binding interface for the calcium sensor GCAP1
- Plasma Membrane Calcium ATPases Drive Cytoplasmic Acidification and Photoreceptor Degeneration in Retinitis Pigmentosa
- Muscle stem cells produce a protective Fibrillin-1 matrix to prevent precocious activation
- Phosphorylation of the mitochondrial calcium uniporter beta subunit matrix domain locks a conformation that suppresses mitochondrial calcium flux
BibTeX
@article{kawashima2026lipid,
title = {{The lipid raft marker flotillin FloA drives relocalization of the plasma membrane H⁺-ATPase PmaA as a protective response to calcium stress}},
author = {Moemi Kawashima and Thomas Krüger and Maira Rosin and Sophie Tröger-Görler and Thorsten Heinekamp and Axel A. Brakhage},
journal = {PLOS Genetics},
year = {2026},
month = oct,
doi = {10.1371/journal.pgen.1012147},
url = {https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1012147},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - The lipid raft marker flotillin FloA drives relocalization of the plasma membrane H⁺-ATPase PmaA as a protective response to calcium stress
AU - Moemi Kawashima
AU - Thomas Krüger
AU - Maira Rosin
AU - Sophie Tröger-Görler
AU - Thorsten Heinekamp
AU - Axel A. Brakhage
PY - 2026
DA - 2026/10/29
JO - PLOS Genetics
DO - 10.1371/journal.pgen.1012147
UR - https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1012147
AB - Biological membranes are laterally heterogeneous and contain specialized microdomains called lipid rafts. Lipid rafts serve as organizational platforms that cluster signaling molecules or modulate membrane protein conformation through their unique lipid environment. There are specific lipid raft marker proteins whose functions remain obscure. One of these proteins is flotillin which has been linked to endocytosis. Here, we investigated the regulation and function of FloA, the sole flotillin homolog in the model fungus Aspergillus nidulans. FloA expression is specifically upregulated in response to calcium stress, which is a regulatory pattern also conserved in Aspergillus fumigatus. BioID proximity labeling revealed that A. nidulans FloA physically interacts with proteins in the endocytic pathway as well as another lipid raft marker, the plasma membrane H+-ATPase PmaA. Under calcium stress, PmaA undergoes internalization from the cytoplasmic membrane. However, when floA is deleted, PmaA internalization is prevented, resulting in cell death. This phenotype of the ΔfloA strain could be mimicked by treating the cells with an endocytosis inhibitor during calcium stress. Together, we demonstrate that FloA is essential for the internalization of PmaA during calcium stress, a process that prevents intracellular calcium overload and promotes cell viability. Our results also provide further evidence for flotillin-assisted endocytosis. Author summary: Lipids and proteins in a cell membrane can cluster together in small regions often called “lipid rafts”, which help the cell interact with its surroundings. Lipid rafts can bring receptors together or influence how membrane proteins behave. Flotillin is a protein often found within lipid rafts, but its exact role is not well understood. Instead of using complex mammalian systems, we studied flotillins in the fungus Aspergillus nidulans, which is a simpler model organism that allows for a better understanding of cellular processes. We found that more flotillins are produced when the fungus is exposed to calcium stress. When flotillins were missing, the cells were unable to remove the protein PmaA from the cell membrane during calcium stress. As a result, the fungus could not cope with the calcium stress and eventually died. Therefore, we propose that flotillins are important for the fungus to reorganize its membranes and coping with calcium stress.
SN - 1553-7404
SN - 1553-7390
ER -