Loop A is critical for the functional interaction of two plasma membrane aquaporins

CINTIA JOZEFKOWICZ; PABLO ROSI; LORENA SIGAUT; FLORENCIA SCOCHERA; LIA PIETRASANTA; GABRIELA AMODEO ; KARINA ALLEVA

Buzios

Congreso; II Latin American Federation of Biophysical Societies Congress/ XXXVII Brazilian Biophysical Society Congress; 2012

Latin American Federation of Biophysical

Objectives Functional properties among plant membrane aquaporins PIP1 and PIP2 is thought to be a consequence of physical interaction of monomers to form heterotetramers. However, PIPs structural elements involved in monomer-monomer contact are not elucidated. We focused our study in Beta vulgaris PIP2 loop A as relevant for PIP1-PIP2 interaction. Methods BvPIP1;1, BvPIP2;2, BvPIP2;1 and BvPIP2;1 mutants were studied in terms of their functional interaction by means of co-injection of PIP cRNA in Xenopus laevis oocytes. Confocal fluorescence microscopy was used to localize PIP isoforms tagged with fluorescence proteins in oocytes. Molecular Dynamics Simulation (MDS) was performed to analyze BvPIP2;1 loop A mobility. Results BvPIP1;1 interact with BvPIP2;2 since when they are co-expressed: i- BvPIP1;1 localization changes from an intracellular position to the plasma membrane , ii- both water transport (Pf)and pH inhibition are increased. Results of BvPIP1;1 and BvPIP2;1 co-expression show: i- BvPIP1;1 stays in the interior of the cell, ii- the same Pf values and pH inhibition than BvPIP2;1 alone. However interaction with BvPIP1;1 is restored when two residues of BvPIP2;1 loop A are mutated. MDS of BvPIP2;1 loop A reveal that within the tetramer each monomer presents a highly mobile loop A that could provide monomer-monomer interaction. Conlusion This contribution unravels how PIP2 and PIP1 interact to form functional heterooligomeric assembles. BvPIP2;1 loop A is relevant for the interaction with BvPIP1;1 and the monomer composition of PIP heterotetramers determinates their functional properties.