Title
The ataxia related G1107D mutation of the plasma membrane Ca2 + ATPase isoform 3 affects its interplay with calmodulin and the autoinhibition process
Author
Tito Calì, Martina Frizzarin, Laura Luoni, Francesco Zonta, Sergio Pantano, Carlos Cruz, Maria Cristina Bonza, Ilenia Bertipaglia, Maria Ruzzene, Maria Ida De Michelis, Nunzio Damiano, Oriano Marin, Ginevra Zanni, Giuseppe Zanotti, Marisa Brini, Raffaele Lopreiato, Ernesto Carafoli
Year
2016
Journal
Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease
Abstract
The plasma membrane Ca2 + ATPases (PMCA pumps) have a long, cytosolic C-terminal regulatory region where a calmodulin-binding domain (CaM-BD) is located. Under basal conditions (low Ca2 +), the C-terminal tail of the pump interacts with autoinhibitory sites proximal to the active center of the enzyme. In activating conditions (i.e., high Ca2 +), Ca2 +-bound CaM displaces the C-terminal tail from the autoinhibitory sites, restoring activity. We have recently identified a G1107D replacement within the CaM-BD of isoform 3 of the PMCA pump in a family affected by X-linked congenital cerebellar ataxia. Here, we investigate the effects of the G1107D replacement on the interplay of the mutated CaM-BD with both CaM and the pump core, by combining computational, biochemical and functional approaches. We provide evidence that the affinity of the isolated mutated CaM-BD for CaM is significantly reduced with respect to the wild type (wt) counterpart, and that the ability of CaM to activate the pump in vitro is thus decreased. Multiscale simulations support the conclusions on the detrimental effect of the mutation, indicating reduced stability of the CaM binding. We further show that the G1107D replacement impairs the autoinhibition mechanism of the PMCA3 pump as well, as the introduction of a negative charge perturbs the contacts between the CaM-BD and the pump core. Thus, the mutation affects both the ability of the pump to optimally transport Ca2 + in the activated state, and the autoinhibition mechanism in its resting state.
Instrument
J-815
Keywords
Circular dichroism, Secondary structure, Chemical stability, Thermal stability, Biochemistry