title: Membrane protein Rim21 plays a central role in sensing ambient pH in Saccharomyces cerevisiae.
abstract: External alkalization activates the Rim101 pathway in Saccharomyces cerevisiae. In this pathway, three integral membrane proteins, Rim21, Dfg16, and Rim9, are considered to be the components of the pH sensor machinery. However, how these proteins are involved in pH sensing is totally unknown. In this work, we investigated the localization, physical interaction, and interrelationship of Rim21, Dfg16, and Rim9. These proteins were found to form a complex and to localize to the plasma membrane in a patchy and mutually dependent manner. Their cellular level was also mutually dependent. In particular, the Rim21 level was significantly decreased in dfg16Δ and rim9Δ cells. Upon external alkalization, the proteins were internalized and degraded. We also demonstrate that the transient degradation of Rim21 completely suppressed the Rim101 pathway but that the degradation of Dfg16 or Rim9 did not. This finding strongly suggests that Rim21 is the pH sensor protein and that Dfg16 and Rim9 play auxiliary functions through maintaining the level of Rim21 and assisting in its plasma membrane localization. Even without external alkalization, the Rim101 pathway was activated in a Rim21-dependent manner by either protonophore treatment or depletion of phosphatidylserine in the inner leaflet of the plasma membrane, both of which caused plasma membrane depolarization like the external alkalization. Therefore, plasma membrane depolarization seems to be one of the key signals for the pH sensor molecule Rim21.
authors.affiliation: Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo 062-0812, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Obara
authors.forename: Hayashi
authors.initials: H
authors.lastname: Yamamoto
authors.forename: Akio
authors.initials: A
authors.lastname: Kihara
mesh_terms: D020816:Amino Acid Motifs; D002462:Cell Membrane / Q000378:metabolism; D044783:F-Box Proteins / Q000378:metabolism; D017353:Gene Deletion; D006031:Glycosylation; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry; D008055:Lipids / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D011956:Receptors, Cell Surface / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism
chemical_list: D044783:F-Box Proteins; D008051:Lipid Bilayers; D008055:Lipids; C470285:MET30 protein, S cerevisiae; D008565:Membrane Proteins; C115786:RIM9 protein, S cerevisiae; D011956:Receptors, Cell Surface; C547025:Rim21 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D049452:Green Fluorescent Proteins; D043743:Ubiquitin-Protein Ligase Complexes