title: Loop B serine of a plasma membrane aquaporin type PIP2 but not PIP1 plays a key role in pH sensing.
abstract: In the plant kingdom, the plasma membrane intrinsic aquaporins (PIPs) constitute a highly conserved group of water channels with the capacity of rapidly adjusting the water permeability (Pf) of a cell by a gating response. Most evidence regarding this mechanism was obtained by different biophysical approaches including the crystallization of a Spinaca olaracea PIP2 aquaporin (SoPIP2;1) in an open and close conformation. A close state seems to prevail under certain stimuli such as cytosolic pH decrease, intracellular Ca2+concentration increase and dephosphorylation of specific serines. In this work we decided to address whether the state of phosphorylation of a loop B serine - highly conserved in all PIPs - combined with cytosolic acidification can jointly affect the gating response. To achieve this goal we generated loop B serine mutants of two PIP types of Fragaria×ananassa (FaPIP2;1S121A and FaPIP1;1S131A) in order to simulate a dephosphorylated state and characterize their behavior in terms of Pfand pH sensitivities. The response was tested for different co-expressions of PIPs (homo and heterotetramers combining wild-type and mutant PIPs) in Xenopus oocytes. Our results show that loop B serine phosphorylation status affects pH gating of FaPIP2;1 but not of FaPIP1;1 by changing its sensitivity to more alkaline pHs. Therefore, we propose that a counterpoint of different regulatory mechanisms - heterotetramerization, serine phosphorylation status and pH sensitivity - affect aquaporin gating thus ruling the Pfof a membrane that expresses PIPs when fast responses are mandatory.
authors: Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Instituto de Biodiversidad y Biología Experimental (IBBEA, UBA-CONICET), Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina.
authors: Agustín
authors: A
authors: Yaneff
authors: Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina; Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Instituto de Física de Buenos Aires (IFIBA, UBA-CONICET) Buenos Aires, Argentina; Centro de Microscopías Avanzadas (CMA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors: Lorena
authors: L
authors: Sigaut
authors: Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina; Instituto de Investigaciones Farmacológicas (ININFA), Universidad de Buenos Aires, Buenos Aires, Argentina.
authors: Natalia
authors: N
authors: Gómez
authors: Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Instituto de Biodiversidad y Biología Experimental (IBBEA, UBA-CONICET), Buenos Aires, Argentina.
authors: Cecilia
authors: C
authors: Aliaga Fandiño
authors: Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Instituto de Biodiversidad y Biología Experimental (IBBEA, UBA-CONICET), Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina.
authors: Karina
authors: K
authors: Alleva
authors: Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina; Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Instituto de Física de Buenos Aires (IFIBA, UBA-CONICET) Buenos Aires, Argentina; Centro de Microscopías Avanzadas (CMA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors: Lía Isabel
authors: LI
authors: Pietrasanta
authors: Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Instituto de Biodiversidad y Biología Experimental (IBBEA, UBA-CONICET), Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina. Electronic address: amodeo@bg.fcen.uba.ar.
authors: Gabriela
authors: G
authors: Amodeo
mesh_terms: D031230:Ananas; D000818:Animals; D020346:Aquaporins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D031985:Fragaria; D015870:Gene Expression; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D010766:Phosphorylation; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism*; D015398:Signal Transduction; D014867:Water / Q000378:metabolism*; D014981:Xenopus
chemical_list: D020346:Aquaporins; D010940:Plant Proteins; D011994:Recombinant Proteins; D014867:Water; D012694:Serine
keywords: Aquaporin gating; Cytosolic acidification; Heteromerization; Osmotic permeability; Water channel; Water transport