Low and high transport assemblies: modulation of transport in water channels is dependent on the pair of paralogues forming the heterotetramer.

SCOCHERA FLORENCIA; JOZEFKOWICZ CINTIA; CANESSA FORTUNA AGUSTINA; AYUB NICOLAS; BIENERT GERD PATRICK; ALLEVA KARINA

Rio de Janeiro

Congreso; V Latin American Protein Society Meeting (LAPSM); 2016

Latin American Protein Society

Transmembrane channel proteins are highly regulated; in particular, oligomerization is a key event in the modulation of the biological activity of these proteins. All aquaporins (AQP) present a tetramericstructure, where each monomer has a single active pore and most of them assemble as homo-tetramers. In the last years, PIP1 and PIP2 plant AQP paralogues have been intensively studied due to their abilityto hetero-oligomerize with variable isoform stoichiometry. Most PIP1-PIP2 pairs studied until now, show that the physical interaction between both paralogues renders an increase in water transport of thewhole tetramer and a shifting in pH gating. In this work, we described for the first time to our knowledge, that the interaction of a specific pair of PIP1 and PIP2 (from Medicago truncatula) can lead to a heterotetramerwith lower permeability than the PIP2 homo-tetramer, suggesting a novel type of monomer-monomer interaction that promote a decrease in the water transport. We assayed the biophysicalproperties of different MtPIP channels by means of two alternative heterologous expression systems, Xenopus laevis oocytes and Saccharomyces cerevisiae and we find that the interaction of specific pairs ofMtPIP1 and MtPIP2 give rise to hetero-tetramers presenting lower water transport than MtPIP2 expressed alone in a consistent way for both expression systems. These new findings open the possibility of amore complex regulation among PIP paralogues where different regulatory pathways can be established: LTA (low transport assemblies) and HTA (high transport assemblies). These types of arrangements tuneplasma membrane water permeability depending on the hetero-tetramer formed. We are confident that these kind of biophysical studies on intersubunit protein interactions are useful to shed light on howquaternary structures endow AQP hetero-oligomeric channels with specific biological properties depending on the isoform composition.