title: PIP Water Transport and Its pH Dependence Are Regulated by Tetramer Stoichiometry.
abstract: Many plasma membrane channels form oligomeric assemblies, and heterooligomerization has been described as a distinctive feature of some protein families. In the particular case of plant plasma membrane aquaporins (PIPs), PIP1 and PIP2 monomers interact to form heterotetramers. However, the biological properties of the different heterotetrameric configurations formed by PIP1 and PIP2 subunits have not been addressed yet. Upon coexpression of tandem PIP2-PIP1 dimers in Xenopus oocytes, we can address, for the first time to our knowledge, the functional properties of single heterotetrameric species having 2:2 stoichiometry. We have also coexpressed PIP2-PIP1 dimers with PIP1 and PIP2 monomers to experimentally investigate the localization and biological activity of each tetrameric assembly. Our results show that PIP2-PIP1 heterotetramers can assemble with 3:1, 1:3, or 2:2 stoichiometry, depending on PIP1 and PIP2 relative expression in the cell. All PIP2-PIP1 heterotetrameric species localize at the plasma membrane and present the same water transport capacity. Furthermore, the contribution of any heterotetrameric assembly to the total water transport through the plasma membrane doubles the contribution of PIP2 homotetramers. Our results also indicate that plasma membrane water transport can be modulated by the coexistence of different tetrameric species and by intracellular pH. Moreover, all the tetrameric species present similar cooperativity behavior for proton sensing. These findings throw light on the functional properties of PIP tetramers, showing that they have flexible stoichiometry dependent on the quantity of PIP1 and PIP2 molecules available. This represents, to our knowledge, a novel regulatory mechanism to adjust water transport across the plasma membrane.
authors.affiliation: Instituto de Química y Fisicoquímica Biológica Alejandro C. Paladini (IQUIFIB), Universidad de Buenos Aires, Consejo National de Investigaciones Científicas y Técnicas (UBA-CONICET), Buenos Aires, Argentina.
authors.forename: Cintia
authors.initials: C
authors.lastname: Jozefkowicz
authors.affiliation: Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina; Instituto de Física de Buenos Aires (IFIBA), CONICET, Ciudad Universitaria, Buenos Aires, Argentina.
authors.forename: Lorena
authors.initials: L
authors.lastname: Sigaut
authors.affiliation: Instituto de Química y Fisicoquímica Biológica Alejandro C. Paladini (IQUIFIB), Universidad de Buenos Aires, Consejo National de Investigaciones Científicas y Técnicas (UBA-CONICET), Buenos Aires, Argentina; Departamento de Fisicomatemática, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: Florencia
authors.initials: F
authors.lastname: Scochera
authors.affiliation: Instituto de Genética Ewald A. Favret, Centro de Investigación en Ciencias Veterinarias y Agronómicas, Instituto Nacional de Tecnología Agropecuaria (INTA), Castelar, Argentina.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Soto
authors.affiliation: Instituto de Genética Ewald A. Favret, Centro de Investigación en Ciencias Veterinarias y Agronómicas, Instituto Nacional de Tecnología Agropecuaria (INTA), Castelar, Argentina.
authors.forename: Nicolás
authors.initials: N
authors.lastname: Ayub
authors.affiliation: Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina; Instituto de Física de Buenos Aires (IFIBA), CONICET, Ciudad Universitaria, Buenos Aires, Argentina; Centro de Microscopías Avanzadas, Facultad de Ciencias Exactas y Naturales, UBA-CONICET, Buenos Aires, Argentina.
authors.forename: Lía Isabel
authors.initials: LI
authors.lastname: Pietrasanta
authors.affiliation: Departamento de Biodiversidad y Biología Experimental, Instituto de Biodiversidad y Biología Experimental y Aplicada, Facultad de Ciencias Exactas y Naturales, UBA-CONICET, Buenos Aires, Argentina.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Amodeo
authors.affiliation: Instituto de Química y Fisicoquímica Biológica Alejandro C. Paladini (IQUIFIB), Universidad de Buenos Aires, Consejo National de Investigaciones Científicas y Técnicas (UBA-CONICET), Buenos Aires, Argentina.
authors.forename: F Luis
authors.initials: FL
authors.lastname: González Flecha
authors.affiliation: Instituto de Química y Fisicoquímica Biológica Alejandro C. Paladini (IQUIFIB), Universidad de Buenos Aires, Consejo National de Investigaciones Científicas y Técnicas (UBA-CONICET), Buenos Aires, Argentina; Departamento de Fisicomatemática, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Buenos Aires, Argentina. Electronic address: kalleva@ffyb.uba.ar.
authors.forename: Karina
authors.initials: K
authors.lastname: Alleva
mesh_terms: D000818:Animals; D020346:Aquaporins / Q000737:chemistry* / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D002463:Cell Membrane Permeability; D006863:Hydrogen-Ion Concentration; D009995:Osmosis; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism*; D055503:Protein Multimerization; D011522:Protons; D014867:Water / Q000378:metabolism*; D014982:Xenopus laevis / Q000378:metabolism
chemical_list: D020346:Aquaporins; D010940:Plant Proteins; D011522:Protons; D014867:Water