International Journal of Molecular Sciences Review Atomistic Insights of Calmodulin Gating of Complete Ion Channels Eider Núñez y, Arantza Muguruza-Montero y and Alvaro Villarroel * Biofisika Institute (CSIC, UPV/EHU), University of the Basque Country, 48940 Leioa, Spain;
[email protected] (E.N.);
[email protected] (A.M.-M.) * Correspondence:
[email protected]; Tel.: +34-9460-13225 These authors contribute equally to this work. y Received: 18 December 2019; Accepted: 12 February 2020; Published: 14 February 2020 Abstract: Intracellular calcium is essential for many physiological processes, from neuronal signaling and exocytosis to muscle contraction and bone formation. Ca2+ signaling from the extracellular medium depends both on membrane potential, especially controlled by ion channels selective to K+, and direct permeation of this cation through specialized channels. Calmodulin (CaM), through direct binding to these proteins, participates in setting the membrane potential and the overall permeability to Ca2+. Over the past years many structures of complete channels in complex with CaM at near atomic resolution have been resolved. In combination with mutagenesis-function, structural information of individual domains and functional studies, different mechanisms employed by CaM to control channel gating are starting to be understood at atomic detail. Here, new insights regarding four types of tetrameric channels with six transmembrane (6TM) architecture, Eag1, SK2/SK4, TRPV5/TRPV6 and KCNQ1–5, and its regulation by CaM are described structurally. Different CaM regions, N-lobe, C-lobe and EF3/EF4-linker play prominent signaling roles in different complexes, emerging the realization of crucial non-canonical interactions between CaM and its target that are only evidenced in the full-channel structure.