FIGURE 6.

KvAP-based model of the Shaker inner-helices bundle obtained by MCM without using the advantage of the channel fourfold symmetry. (A and B) Side and cytoplasmic views of superposition of KvAP x-ray structure (red) and locked-open Shaker mutant Val-476-Cys (green). The side chains of Cys-476 and His-486 are shown as sticks. K⁺ and Cd²⁺ ions are shown as spheres. The inner helices bend smoothly at residues N-terminal to the PVP motif. (C and D) Changes of backbone torsions in four subunits observed during the simulated locking of the open channel starting from the KvAP-based conformation. Largest changes of Φ are at Leu-472 and Pro-473 and moderate changes are in segments both N- and C-terminal to the PVP motif. Largest changes of Ψ are at Ala-471, whose backbone oxygen lacks the helical H-bond. Changes at Ile-478 through His-486 are not shown because torsions were restrained in alpha-helical conformation. Changes at Leu-461 are not shown because this residue was constrained at conformation seen in KvAP.