Aluminium interacts differently with lipid bilayers and modulates the Plasma membrane calcium ATPase (PMCA) activity

DE SAUTU, MARILINA; ROSSI, JP; SCANAVACHI, GUSTAVO; ITRI, ROSANGELA; FERREIRA-GOMES, MARIELA; MANGIALAVORI, IRENE CECILIA

San Diego

Congreso; 64th Annual Biophysical Society Meeting; 2020

Biophysical Society

PMCA is a P-ATPase involved in the regulation of the cell calcium homeostasis transporting Ca2+ from cytoplasm towards the extracellular medium. Like other integral membrane proteins operates surrounded by a complex and dynamic lipid bilayer, and its activity largely depends on the lipids. Aluminium (Al3+ and other soluble species) is environmentally ubiquitous, providing human exposure and neurotoxic effects in humans. 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.The aim of this work is to understand the aluminium effect on the lipidic environment of PMCA. Aluminium would have distinct effect depending on the lipid composition of the cell membrane where 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 evaluated how free aluminium was modified by interacting with the different lipids. To evaluate other biophysical changes on the lipid bilayers we did Small Angle X-ray Scattering (SAXS) experiments and we studied how the lipidic environment was changing alongside different molar fractions. In turn, we used Laurdan probe to evaluate changes in the membrane phase properties.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.