The Rim101 pathway mediates adaptation to external alkalization and altered lipid asymmetry: hypothesis describing the d
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MINI-REVIEW
Perspective The Rim101 pathway mediates adaptation to external alkalization and altered lipid asymmetry: hypothesis describing the detection of distinct stresses by the Rim21 sensor protein Keisuke Obara1 · Takumi Kamura1 Received: 31 August 2020 / Revised: 21 October 2020 / Accepted: 30 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Yeast cells adapt to alkaline conditions by activating the Rim101 alkali-responsive pathway. Rim21 acts as a sensor in the Rim101 pathway and detects extracellular alkalization. Interestingly, Rim21 is also known to be activated by alterations involving the lipid asymmetry of the plasma membrane. In this study, we briefly summarize the mechanism of activation and the signal transduction cascade of the Rim101 pathway and propose a hypothesis on how Rim21 is able to detect distinct signals, particularly external alkalization, and altered lipid asymmetry. We found that external alkalization can suppress transbilayer movements of phospholipids between the two leaflets of the plasma membrane, which may lead to the disturbance of the lipid asymmetry of the plasma membrane. Therefore, we propose that external alteration is at least partly sensed by Rim21 through alterations in lipid asymmetry. Understanding this activation mechanism could greatly contribute to drug development against fungal infections. Keywords Plasma membrane · Lipid asymmetry · Alkali · Rim101 pathway · Stress response · Yeast
The Rim101 pathway is activated by external alkalization and alterations in the lipid asymmetry of the plasma membrane Cells are continually exposed to a wide variety of environmental stresses and need to constantly cope with such stresses for survival. The budding yeast, Saccharomyces cerevisiae, is a unicellular organism that responds to environmental changes in a cell-autonomous manner. S. cerevisiae as well as some filamentous and pathogenic fungi can grow over a wide ambient pH range, and their cellular responses to external alkalization serve as suitable models Communicated by M. Kupiec. * Keisuke Obara [email protected]‑u.ac.jp * Takumi Kamura [email protected]‑u.ac.jp 1
Division of Biological Science, Graduate School of Science, Nagoya University, Furo‑cho, Chikusa‑ku, Nagoya 464‑8602, Japan
for studying adaptation to stress. These cells adapt to alkaline conditions via activation of the Rim101 pathway (Davis 2009; Peñalva and Arst 2004; Selvig and Alspaugh 2011) (Fig. 1). It is interesting to note that the Rim101 pathway is also activated by alterations in the lipid asymmetry of the plasma membrane (Ikeda et al. 2008). The lipid molecules in the lipid bilayer of the plasma membrane are distributed unevenly between the inner and outer leaflets of the membrane (Devaux 1991; Verkleij and Post 2000), thus resulting in the formation of asymmetric biomembranes. For instance, phosphatidylserine and phosphatidylethanolamine are mostly confined to the inner leaflet of the membrane, while complex sphingolipids are distributed in
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