PIP Water Transport and Its pH Dependence Are Regulated by Tetramer Stoichiometry

CINTIA JOZEFKOWICZ; LORENA SIGAUT; FLORENCIA SCOCHERA; GABRIELA SOTO; NICOLAS AYUB; LIA PIETRASANTA; GABRIELA AMODEO; F. LUIS GONZÁLEZ FLECHA; KARINA ALLEVA

BIOPHYSICAL JOURNAL

CELL PRESS

Lugar: United States; Año: 2016 vol. 110 p. 1312 - 1321

0006-3495

Biophysical JournalVolume 110, Issue 6, 29 March 2016, Pages 1312-1321PIP Water Transport and Its pH Dependence Are Regulated by Tetramer Stoichiometry (Article)Jozefkowicz, C.a, Sigaut, L.bc, Scochera, F.ad, Soto, G.e, Ayub, N.e, Pietrasanta, L.I.bcf, Amodeo, G.g, González Flecha, F.L.a, Alleva, K.ad a 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 b Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina c Instituto de Física de Buenos Aires (IFIBA), CONICET, Ciudad Universitaria, Buenos Aires, Argentina d Departamento de Fisicomatemática, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Buenos Aires, Argentina e Instituto de Genética Ewald A. Favret, Centro de Investigación en Ciencias Veterinarias y Agronómicas, Instituto Nacional de Tecnología Agropecuaria (INTA), Castelar, Argentina f Centro de Microscopías Avanzadas, Facultad de Ciencias Exactas y Naturales, UBA-CONICET, Buenos Aires, Argentina g 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 Hide additional affiliationsView references (39)AbstractMany 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.