Aquaporins: current understanding and new challenges

AMODEO, GABRIELA

San Luis

Conferencia; XLVIII Reunión Anual de la Sociedad de Biofísica, 27 al 29 de Noviembre de 2019, Universidad de San Luis, San Luis.; 2019

SAB

Aquaporins (AQPs) are small integral membrane channels that have challenged water transport exchange capacity across biological membranes throughout all kingdoms. Despite they all share common structural features (assembled as homo/heterotetramers in which each monomer has its own permeable pathway), their multiple isoforms are distinguished for their high diversity in cell localization, transport selectivity (e.g. small solutes and/or gases) as well as their regulatory properties. The invaluable number of high-resolution X-ray structures of AQPs from different organisms along with molecular dynamics simulation studies has contributed to understand clue structural mechanisms by which water flux through AQPs is controlled. This has paved the road for genetic and physiological approaches and, all this combination is helping to close the ?structure-function gap?, confirming their specific contribution both in the animal and plant field. The aim of our work is to contribute to the study of plant AQPs addressing regulatory mechanisms that can rapidly adjust water membrane permeability (Pf). In particular, plant plasma membrane intrinsic proteins (PIPs) seems to play an important role in controlling (Pf). These PIP aquaporins also represent a highly abundant and conserved subfamily divided into two subgroups: PIP1 and PIP2. In terms of their function, all PIPs show capacity to rapidly adjust the Pf by means of a gating response. In our work, we specifically addressed the cytosolic acidification as a stimuli that favors the close state. Many PIP1s also show another feature: they fail to reach the PM when expressed alone, but they can succeed if they are coexpressed with a PIP2. Therefore, in terms of activity, PIP aquaporins can rapidly adjust membrane water permeability by means of two mechanisms: channel gating and channel translocation of PIP subunits (PIP1 and PIP2, organized -or not- in mixed tetramers). Evidences indicate that these mechanisms are not only highly conserved among species but their juxtaposition enhances the dynamics of the response. In this sense our findings also contribute to describe regulatory mechanisms that cannot be attributed to independent monomers. Finally, the functional properties of this interaction and physiological consequences are addressed in order to understand the relevance of the cell-to-cell pathway in the plant hydraulic dynamics not only as a physiological challenge but also as a response to adverse plant environmental conditions.