Effect of the lipid environment on plasma membrane Ca2+ ATPase in the absence of its auxiliary subunit neuroplastin/basigin

CAMILA BRUNO; CECILIA SOUTO GUEVARA; MARILINA DE SAUTU; JUAN PABLO ROSSI; IRENE MANGIALAVORI

Congreso; XLIX Reunión Anual de la Sociedad Argentina de Biofísica; 2021

The plasma membrane Ca2+-ATPase (PMCA) is a highly regulated transporter responsible for the extrusion of Ca2+ from all eukaryotic cells. PMCA isoforms are expressed in different tissues and perform their function through the adjustment Ca2+ concentration in membrane microdomains that are related in Ca2+ signaling events. In humans, the variants PMCA1 and 4 are ubiquitously expressed whereas PMCA2 and 3 are expressed in specialized tissues. ATPase activity is modulated by several modulators being calmodulin one of the most effective by binding to the C-terminal domain of PMCA.It has recently been discovered that neuroplastin and basigin, two glycoproteins, would act as a mandatory subunit of PMCA1. PMCA forms a heterodimer with neuroplastin or basigin depending on the neuroplastin/basigin ratio in each tissue2. The interaction of PMCA with neuroplastin/basigin is essential for its correct targeting towards the plasma membrane. It has also been proposed that basigin or neuroplastin would be necessary for PMCA to be active4, but these studies remain controversial.The aim of this work was to study the effect of the mandatory subunit on activity of PMCA in the activated and auto-inhibited states. To this end, we used the PMCA of human erythrocytes as a model, whose majority variant is PMCA4. Our results showed that: (1) Basigin, but not neuroplastin, was present after purification of PMCA, (2) PMCA reconstituted in detergent micelles, was inactive in the absence of basigin; (3) PMCA reconstituted in mixed micelles of detergent-phospholipids, was active in the absence of basigin, (4) The apparent affinity for Ca2+ and Mg2+ of PMCA in erythrocytes plasma membranes was similar to that PMCA reconstituted in mixed micelles. This suggests that PMCA´s activity and Ca2+ apparent affinity depend on the biophysical characteristic of the lipid environment in the absence of its auxiliary subunit.