Calmodulin antagonizes amyloid-β peptides-mediated inhibition of brain plasma membrane Ca(2+)-ATPase

Abstract

The synaptosomal plasma membrane Ca(2+)-ATPase (PMCA) plays an essential role in regulating intracellular Ca(2+) concentration in brain. We have recently found that PMCA is the only Ca(2+) pump in brain which is inhibited by amyloid-β peptide (Aβ), a neurotoxic peptide implicated in the pathology of Alzheimer's disease (AD) [1], but the mechanism of inhibition is lacking. In the present study we have characterized the inhibition of PMCA by Aβ. Results from kinetic assays indicate that Aβ aggregates are more potent inhibitors of PMCA activity than monomers. The inhibitory effect of Aβ could be blocked by pretreating the purified protein with Ca(2+)-calmodulin, the main endogenous activator of PMCA, and the activity of truncated PMCA lacking the calmodulin binding domain was not affected by Aβ. Dot-overlay experiments indicated a physical association of Aβ with PMCA and also with calmodulin. Thus, calmodulin could protect PMCA from inhibition by Aβ by burying exposed sites on PMCA, making them inaccessible to Aβ, and also by direct binding to the peptide. These results suggest a protective role of calmodulin against neuronal Ca(2+) dysregulation by PMCA inhibition induced by Aβ.