α‐Actinin‐1 promotes activity of the L‐type Ca2+ channel Cav1.2

• Published in: The EMBO journal 2020-03, Vol.39 (5), p.n/a
• Main Authors: Turner, Matthew, Anderson, David E, Bartels, Peter, Nieves‐Cintron, Madeline, Coleman, Andrea M, Henderson, Peter B, Man, Kwun Nok Mimi, Tseng, Pang‐Yen, Yarov‐Yarovoy, Vladimir, Bers, Donald M, Navedo, Manuel F, Horne, Mary C, Ames, James B, Hell, Johannes W
• Format: Article
• Language: English
• Subjects: Actinin; Binding; Calcium channels (voltage-gated); Calcium ions; Calcium-binding protein; Calmodulin; Cell surface; Channel gating; Channel opening; Contraction; Coupling; EF-hand; EMBO20; EMBO27; gating charge; Gene expression; IQ motif structure; Localization; Mutation; NMR; Nuclear magnetic resonance; open probability; Potassium; Residues; Structure-function relationships; surface expression
• ISSN: 0261-4189; 1460-2075
• DOI: 10.15252/embj.2019102622

The L‐type Ca 2+ channel Ca V 1.2 governs gene expression, cardiac contraction, and neuronal activity. Binding of α‐actinin to the IQ motif of Ca V 1.2 supports its surface localization and postsynaptic targeting in neurons. We report a bi‐functional mechanism that restricts Ca V 1.2 activity to its target sites. We solved separate NMR structures of the IQ motif (residues 1,646–1,664) bound to α‐actinin‐1 and to apo‐calmodulin (apoCaM). The Ca V 1.2 K1647A and Y1649A mutations, which impair α‐actinin‐1 but not apoCaM binding, but not the F1658A and K1662E mutations, which impair apoCaM but not α‐actinin‐1 binding, decreased single‐channel open probability, gating charge movement, and its coupling to channel opening. Thus, α‐actinin recruits Ca V 1.2 to defined surface regions and simultaneously boosts its open probability so that Ca V 1.2 is mostly active when appropriately localized. Synopsis Regulation of the L‐type voltage‐gated Ca 2+ channel Ca V 1.2 by the EF hand proteins apo‐calmodulin (apoCaM) and α‐actinin remains debated. Here, structure‐function analyses report a dual role for α‐actinin‐1 in both instructing Ca V 1.2 cell surface localisation and increasing channel activity. NMR structures of ‐actinin‐1 and apoCaM EF3/4 hands bound to the Ca V 1.2 IQ motif identify distinct residues critical for binding. Ca V 1.2 IQ mutations impairing α‐actinin‐1 binding decrease channel open probability. Ca V 1.2 IQ mutations impairing apoCaM binding do not alter channel activity. α‐Actinin‐1 binding increases coupling of Ca V 1.2 gating charge movement to channel opening. Graphical Abstract The scaffold protein α‐actinin is a positive regulator of Ca V 1.2 channel open probability and gating.