Plasma Membrane Calcium ATPase (PMCA) activity is modulated by the biophysical properties of the surrounding bilayer

MARILINA DE SAUTU; GUSTAVO SCANAVACHI; MARIELA S. FERREIRA-GOMES; JUAN PABLO F.C. ROSSI; ROSANGELA ITRI; IRENE C MANGIALAVORI

Congreso; 20th International Union for Pure and Applied Biophysics (IUPAB), 50th Annual Meeting of the SBBq, 45th Congress of SBBf and 13th Congress SBBN, virtually, Brazil, on October 4th to 8th.; 2021

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. 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 demonstrated that aluminium inhibits PMCA activity preventing the dephosphorylation of the pump.The aim of this work is to understand the effect of the surrounding bilayer on the PMCA activity and on the effect of the aluminium. 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. 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 performed small Angle X-ray scattering (SAXS) experiments for studying how the lipidic environment was changing alongside different molar fractions and also in the presence of aluminium. In turn, we evaluate changes in the membrane phase properties using two fluorescent probes, laurdan and merocyanine 540. The results show a biphasic effect of activation and inhibition of the pump that depended on the molar fraction of phospholipids. 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 and influences the biophysical properties that in turn, affected the PMCA activity.