Plasma membrane calcium ATPase (PMCA) activity is modulated by aluminum through its effects on the lipid bilayer

DE SAUTU, MARILINA; SCANAVACHI GUSTAVO; FERREIRA GOMES, MARIELA; ROSSI JPFC; ROSANGELA ITRI; I MANGIALAVORI

Santos

Congreso; Congresso Sociedade Brasileira de Biofisica; 2019

Aluminum (Al3+ and other soluble species) is environmentally ubiquitous, providing human exposure and neurotoxic effects in humans and animals. The mechanisms proposed to explain aluminum toxicity are linked to changes in the cellular calcium homeostasis. Recently, we demonstrated that aluminum inhibits PMCA activity by preventing the dephosphorylation of the pump [1]. PMCA is a P-ATPase involved in the regulation of the cell calcium homeostasis transporting Ca2+ from cytoplasm towards the extracellular medium against the electrochemical gradient. PMCA like other integral membrane proteins operates surrounded by a complex and dynamic lipid bilayer, and the activity of this pump largely depends on its phospholipids [2]. In previous works, we showed that AlCl3 inhibits calcium efflux mediated by PMCA in HEK293T cells. The aim of this work is to understand the effect of aluminum on the lipid environment of PMCA. Aluminum would have distinctive 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 with or without the presence of aluminum. Using small angle X-ray scattering (SAXS) we studied how the lipidic environment was changing alongside different molar fractions at different concentrations of aluminum. Further, we evaluate how aluminum interacts with different phospholipids using the specific fluorescent probe, lumogallion. The inhibition of the pump by aluminum depends 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 aluminum interacts with the micelles, in agreement with lumogallion fluorescence changes. Acknowledgement: This work was supported by ANPCYT PICT 2014 0065, CONICET PIP 0250 and Universidad de Buenos Aires: 20020130100254B, LNLS, CAPES, CNPq, FAPESP.[1] De Sautu M et al. BBA-Biomembrane (2018) 860(8):1580-1588. doi: 10.1016/j.bbamem.2018.05.014 [2] Pignataro, M. F et al (2015) Modulation of plasma membrane Ca2+-ATPase by neutral phospholipids: effect of the micelle-vesicle transition and the bilayer thickness. The Journal of biological chemistry, 290(10), 6179?6190. doi:10.1074/jbc.M114.