FaPIP2-FaPIP1 heterotetramers and FaPIP2 homotetramers show different sensitivity to mechanical regulation

GALIZIA, LUCIANO; OZU, MARCELO; GUASTAFERRI, FLORENCIA V.; SUTKA, MOIRA; GOLDMAN, RAMIRO P

San Luis

Congreso; Reunion Anual de la Sociedad Argentina de Biofísica; 2019

Sociedad Argentina de Biofisica

FaPIP2;1 is a high Pf strawberry water channel that forms heterotetramers with FaPIP1;1, and can be regulated by pH, by means of a cooperative mechanism. In our previous work we studied the transport properties of FaPIP2;1 and found that this water channel responds just like a mechanosensitive aquaporin. It is hypothesized that this mechanism would also be cooperative involving the four monomers. The study of pH sensitivity with FaPIP2;1-FaPIP1;1 heterotetramers demonstrated that the interactions between different subunits modify the cooperativity among monomers. We consider FaPIP2;1-FaPIP1;1 heterotetramers would be a good model to study the cooperativity in mechanical regulation of aquaporins. Our hypothesis is that FaPIP2;1-FaPIP1;1 heterotetramers show different sensitivity to mechanical regulation than FaPIP2;1 homotetramers. By means of the same methods followed in previous works, we determined the water flux (Jw) and osmotic permeability coefficient (Pf) of xenopus oocytes injected with a mix of cRNA of FaPIP2;1 and FaPIP1;1 (1:3). Each oocyte was injected with 5 ng of cRNA and subjected to different osmotic gradients (Äosm) created with mannitol. On our most recent results the Jw (nl.s-1) measured in oocytes subjected to 40, 90 and 140 mOmol.Kgw-1 was 0.30 ± 0.10 (n=6), 0.59 ± 0.10 (n=8) and 1.13 ± 0.07 (n=8), respectively. These results show a linear Jw-Äosm relationship (R2>0.98), and the same Pf value, of about 2.0x10-2 cm.s-1, in all tested conditions. In comparison, FaPIP2;1 homotetramers show deviations from linearity for said relationships, a typical behavior of mechanosensitive aquaporins. That being so, it can be said that FaPIP2;1-FaPIP1;1 heterotetramers appear to be at least less sensitive to membrane tension changes than FaPIP2;1 homotetramers.