CONICET | Buscador de Institutos y Recursos Humanos

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 tetrameric structure, 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 ability to 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 the whole 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 hetero-tetramer with 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 biophysical properties 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 of MtPIP1 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 a more 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 tune plasma 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 how quaternary structures endow AQP hetero-oligomeric channels with specific biological properties depending on the isoform composition.