Fig. 1.

Crystal structure of the C-terminal pre-IQ-IQ fragment from the Ca_V1.2 α₁ subunit. CaM N-lobes/domains are tan; C-lobes light blue; Ca²⁺ ions are gold spheres. Ca_V1.2 fragments (I and II) are blue to orange rainbow starting from the N termini (marked with N); the IQ domain for fragment I is red. Loop regions, the IQ domain for fragment II, and the C-domain of CaM IV are not seen in the density and are modeled, by analogy with fragment I and CaM III, as thin light gray lines for reference. The N- and C-lobes of the extended form of CaMs I and II bridging the pre-IQ segments are separated by ≈15 Å, whereas those of CaM III bound to the IQ motif of Ca_VI fragment make contacts. Figs. 1 and 2 were made with PyMOL (www.pymol.org).