Download MendeleyCa2+ regulation in the Na+/Ca2+ exchanger features a dual electrostatic switch mechanism.
Hilge, M., Aelen, J., Foarce, A., Perrakis, A., Vuister, G.W.(2009) Proc Natl Acad Sci U S A 106: 14333-14338
- PubMed: 19667209
- DOI: https://doi.org/10.1073/pnas.0902171106
- Primary Citation of Related Structures:
2KLS, 2KLT - PubMed Abstract:
Regulation of ion-transport in the Na(+)/Ca(2+) exchanger (NCX) occurs via its cytoplasmic Ca(2+)-binding domains, CBD1 and CBD2. Here, we present a mechanism for NCX activation and inactivation based on data obtained using NMR, isothermal titration calorimetry (ITC) and small-angle X-ray scattering (SAXS). We initially determined the structure of the Ca(2+)-free form of CBD2-AD and the structure of CBD2-BD that represent the two major splice variant classes in NCX1. Although the apo-form of CBD2-AD displays partially disordered Ca(2+)-binding sites, those of CBD2-BD are entirely unstructured even in an excess of Ca(2+). Striking differences in the electrostatic potential between the Ca(2+)-bound and -free forms strongly suggest that Ca(2+)-binding sites in CBD1 and CBD2 form electrostatic switches analogous to C(2)-domains. SAXS analysis of a construct containing CBD1 and CBD2 reveals a conformational change mediated by Ca(2+)-binding to CBD1. We propose that the electrostatic switch in CBD1 and the associated conformational change are necessary for exchanger activation. The response of the CBD1 switch to intracellular Ca(2+) is influenced by the closely located cassette exons. We further propose that Ca(2+)-binding to CBD2 induces a second electrostatic switch, required to alleviate Na(+)-dependent inactivation of Na(+)/Ca(2+) exchange. In contrast to CBD1, the electrostatic switch in CBD2 is isoform- and splice variant-specific and allows for tailored exchange activities.
Organizational Affiliation:
Protein Biophysics, Institute for Molecules and Materials, Radboud University Nijmegen, 6525 GA Nijmegen, The Netherlands. markhilge@mac.com
