A defined aquaporin stoichiometry in order to understand water permeability and pH sensitivity

AGUSTÍN YANEFF; LORENA SIGAUT; MERCEDES MARQUEZ; KARINA ALLEVA; LÍA PIETRASANTA; GABRIELA AMODEO

Mendoza

Congreso; XLVIII Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular; 2012

Objectives Plant plasma membrane aquaporins are classified in PIP1 and PIP2 subgroups, all showing the ability to block water permeation after cytosolic acidification. While PIP2 prevails as a homotetrameric structure, most of the PIP1 request co-expression with a PIP2 to reach the plasma membrane and thus enhanced the osmotic water permeability (Pf). Our working hypothesis is that FaPIP1;1, interacts with FaPIP2;1 in a defined stoichiometry providing heterotetrameric units able to modify both Pf and pH sensitivity. Methods Water transport and PIPs pH regulation were studied in Xenopus oocyte heterologous system employing a N228DFaPIP2;1 mutant. All EYFP tagged PIPs were localized by fluorescent confocal microscopy. Results FaPIP1;1 cannot reach the PM unless it is co-expressed with native FaPIP2;1 or N228D FaPIP2;1. N228DFaPIP2;1 can only achieve PM if it is co-expressed with FaPIP1;1. The pH sensitivity remains constant when different ratios of FaPIP1;1 and FaPIP2;1 or N228D are co-expressed, but differ from the pH sensitivity of FaPIP2;1 expressed alone. The maximum Pf achieved is constant when different ratios of FaPIP1;1 and FaPIP2;1 cRNA are injected but variable when in the ratios FaPIP2;1 is replaced by N228D. Conclusion Results establish a possible stoichiometry for FaPIP1;1-FaPIP2;1 that defines the pH sensitivity of the membrane water transport.