Abstract
Yeast responds to alterations in plasma membrane lipid asymmetry and external alkalization via the sensor protein Rim21 in the Rim101 pathway. However, the sensing mechanism used by Rim21 remains unclear. Here, we found that the C-terminal cytosolic domain of Rim21 (Rim21C) fused with GFP was associated with the plasma membrane under normal conditions but dissociated upon alterations in lipid asymmetry or external alkalization. This indicates that Rim21C contains a sensor motif. Rim21C contains multiple clusters of charged residues. Among them, three consecutive Glu residues (EEE motif) were essential for Rim21 function and dissociation of Rim21C from the plasma membrane in response to changes in lipid asymmetry. In contrast, positively charged residues adjacent to the EEE motif were required for Rim21C to associate with the membrane. We therefore propose an "antenna hypothesis," in which Rim21C moves to or from the plasma membrane and functions as the sensing mechanism of Rim21.
Highlights
In the plasma membrane lipid bilayer, lipid molecules are distributed unevenly between the inner and outer leaflets
Rim21C Dissociates from the Plasma Membrane in Response to Altered Lipid Asymmetry—To gain insight into the molecular mechanism by which Rim21 senses alterations in lipid asymmetry, we first focused on the C-terminal cytosolic region of Rim21 (Rim21C), where charged amino acid residues are highly enriched (Fig. 1A)
We have demonstrated that Rim21C contains a region that functions to sense lipid asymmetry and external alkalization (Figs. 1 and 2)
Summary
Yeast responds to alterations in plasma membrane lipid asymmetry and external alkalization via the sensor protein Rim in the Rim101 pathway. We found that the C-terminal cytosolic domain of Rim (Rim21C) fused with GFP was associated with the plasma membrane under normal conditions but dissociated upon alterations in lipid asymmetry or external alkalization. This indicates that Rim21C contains a sensor motif. Three consecutive Glu residues (EEE motif) were essential for Rim function and dissociation of Rim21C from the plasma membrane in response to changes in lipid asymmetry. We proposed an “antenna hypothesis” for the sensing mechanism employed by Rim
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