Plasma Membrane Calcium ATPase (PMCA) activity is modulated by aluminium due to its differential interaction with lipid bilayers

MARILINA DE SAUTU; SCAVANACHI G; CANDELARIA DE LA FUENTE1§, LAURA VANAGAS1§, IRENE MANGIALAVORI1, MARIELA FERREIRA GOMES1, MARIANELA DALGHI1, ROLANDO C. ROSSI1, EMANUEL E. STREHLER2, AND JUAN P.F.C. ROSSI1; ROSSI JUAN P; IRENE MANGIALAVORI

CABA

Congreso; Primeras Jornadas Virtuales SAB 2020; 2020

SAB

PMCA is a P-ATPase involved in the regulation of the cell calcium homeostasis transporting Ca2+ from cytoplasm towards the extracellular medium. PMCA like other integral membrane proteins operates surrounded by a complex and dynamic lipid bilayer, and its activity largely depends on the lipids [1].  Aluminium (Al3+ and other soluble species) is environmentally ubiquitous, providing human exposure and neurotoxic effects in humans and animals. The mechanisms proposed to explain aluminium toxicity are linked to changes in the cellular calcium homeostasis. In previous works, we showed that AlCl3 inhibits calcium efflux mediated by PMCA in HEK293T cells. Also, we demonstrated that aluminium inhibits PMCA activity preventing the dephosphorylation of the pump [2]. The aim of this work is to understand the effect of aluminium on the lipidic environment of PMCA. Aluminium would have distinct effect depending on the lipid composition of the cell membrane where the PMCA is located. To characterize this effect, mixed micelles of phospholipids and detergent (C12E10) were formed at different molar fractions and we measured how PMCA activity varied at different concentration of aluminium. Further, with an aluminum-specific fluorescent probe (Lumogallion) we evaluate how free aluminium is modified by interacting with the different lipids. To evaluate other biophysical changes in the lipid bilayers we use Small Angle X-ray scattering (SAXS) experiments we studied how the lipidic environment was changing alongside different molar fractions at different concentrations of aluminium. In turn, we evaluate changes in the membrane phase properties using the Laurdan probe. The results show a biphasic effect of activation and inhibition of the pump by aluminium depending largely on the composition and concentration of phospholipids surrounding PMCA. SAXS measurements indicate that biophysical changes of the bilayer at different molar fractions could explain the difference in enzymatic activity. Moreover, we demonstrated how aluminium interacts with the micelles, in agreement with lumogallion fluorescence changes.