Fig. 3

Proposed models for the (a) inactive, (b) partially active, and c. fully active states of CaN. The inactive state (a) occurs at basal calcium concentrations and is thought to have the regulatory domain folded onto the B chain binding helix and the N-terminal lobe of CnB1 unbound. The partially active state (b) occurs when calcium is bound to CnB1 but prior to CaM binding. In this state the N-terminal lobe of CnB1 binds to the B chain binding helix, releasing the regulatory domain into a disordered state. The fully active state (c) occurs when holo-CaM has bound to CaN causing the regulatory domain to fold and removing the autoinhbitory domain from the active site