Figure 15.

Homology model of the pore region for the open and closed state of KCa3.1. (Left) Representation of the S5-P-helix-S6 region viewed as a profile illustrating the predicted orientation of Cys²⁷⁶ (yellow) and the L281W mutation (red) in the closed state using the KcsA structure. (Inset) Structure of PCMBS adapted from the crystal structure of PCMBS in complex with the Charcot-Leyden crystal protein (Ackerman et al., 2002). PCMBS is 6.5 Å in length and 9.0 Å in length when the thiol group is included. The color red represents oxygen molecules, yellow (sulfur), cyan (carbon), and white (mercury). (Right) Representation of the S5-P-helix-S6 region viewed as a profile illustrating the predicted orientation of Cys²⁷⁶ (yellow) and the L281W mutation (red) in the open state based upon the structure of rKv1.2. Sequence alignments used for homology modeling can be found in Fig. 5 C. (Inset) Representation of S5 and S6 viewed from the intercellular aspect of the pore to illustrate that Leu²⁸¹ (L281W) is oriented toward S5. Cys²⁷⁶ and L281W from the adjacent subunit are the only residues illustrated to compare the predicted orientation in the closed and open state. The S5 and P-helix are colored green and the S6 helix is colored blue. All residues are illustrated in VDW format. The C-terminal portion of the S5 helix was removed to prevent obscuring the view of L281W.