Insights into voltage-gated calcium channel regulation from the structure of the CaV1.2 IQ domain–Ca2+/calmodulin complex

摘要

Changes in activity-dependent calcium flux through voltage-gated calcium channels (CaVs) drive two self-regulatory calcium-dependent feedback processes that require interaction between Ca²⁺/calmodulin (Ca²⁺/CaM) and a CaV channel consensus isoleucine-glutamine (IQ) motif: calcium-dependent inactivation (CDI) and calcium-dependent facilitation (CDF). Here, we report the high-resolution structure of the Ca²⁺/CaM–CaV1.2 IQ domain complex. The IQ domain engages hydrophobic pockets in the N-terminal and C-terminal Ca²⁺/CaM lobes through sets of conserved ‘aromatic anchors.’ Ca²⁺/N lobe adopts two conformations that suggest inherent conformational plasticity at the Ca²⁺/N lobe–IQ domain interface. Titration calorimetry experiments reveal competition between the lobes for IQ domain sites. Electrophysiological examination of Ca²⁺/N lobe aromatic anchors uncovers their role in CaV1.2 CDF. Together, our data suggest that CaV subtype differences in CDI and CDF are tuned by changes in IQ domain anchoring positions and establish a framework for understanding CaM lobe–specific regulation of CaVs.