Correction to “Ca²⁺ regulation of inositol 1,4,5-trisphosphate receptors: can Ca²⁺ function without calmodulin?”

A–C, Ca²⁺ binding to CaM. A, structure of the C-terminal lobe of CaM with Ca²⁺ bound (PDB code 4CLN). B, Ca²⁺-binding loop of the third EF hand of CaM; the residue mutated to produce CaM with much reduced affinity for Ca²⁺ is shown in red. C, structures of apoCaM (blue; PDB code 1CFC) and Ca²⁺-CaM (red; PDB code 3CLN). D–F, regulation of Ca²⁺ channels by CaM. D, CaM tethered in the C-terminal tail of the L-type Ca²⁺ channels binds Ca²⁺ and thereby acquires the ability to interact with a second CaM-binding site through which CDI is initiated. E, for non–L-type Ca²⁺ channels the two lobes of Ca²⁺ are positioned to respond to different Ca²⁺ signals, the C-lobe preferentially detects Ca²⁺ (red) passing through the channel, whereas the N-lobe responds to global Ca²⁺ signals (blue). F, in RyR1, the tethered C-lobe of CaM moves toward the N-terminal of a CaM-binding region when it binds Ca²⁺ (pink), whereas the N-lobe interacts with a site on a neighboring subunit. The C-lobe provides the essential Ca²⁺ sensor and its movement leads to channel inhibition, possibly by causing rearrangement of the interactions between the subunits. The Cys residues that also mediate cross-linking of subunits are also shown.