Cardiovascular Research Institute, Department of Biochemistry and Biophysics, California Institute for Quantitative Biomedical Research, University of California, San Francisco, 1700 4th St., Box 2532, San Francisco, California 94143-2532, USA.
Changes in activity-dependent calcium flux through voltage-gated calcium channels (Ca(V)s) drive two self-regulatory calcium-dependent feedback processes that require interaction between Ca(2+)/calmodulin (Ca(2+)/CaM) and a Ca(V) channel consensus isoleucine-glutamine (IQ) motif: calcium-dependent inactivation (CDI) and calcium-dependent facilitation (CDF). Here, we report the high-resolution structure of the Ca(2+)/CaM-Ca(V)1.2 IQ domain complex. The IQ domain engages hydrophobic pockets in the N-terminal and C-terminal Ca(2+)/CaM lobes through sets of conserved 'aromatic anchors.' Ca(2+)/N lobe adopts two conformations that suggest inherent conformational plasticity at the Ca(2+)/N lobe-IQ domain interface. Titration calorimetry experiments reveal competition between the lobes for IQ domain sites. Electrophysiological examination of Ca(2+)/N lobe aromatic anchors uncovers their role in Ca(V)1.2 CDF. Together, our data suggest that Ca(V) 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 Ca(V)s.