Publication: Why Does the Inner-Helix Mutation A413C Double the Stoichiometry of Kv1.3 Channel Block by Emopamil but Not by Verapamil?
All || By Area || By Year| Title | Why Does the Inner-Helix Mutation A413C Double the Stoichiometry of Kv1.3 Channel Block by Emopamil but Not by Verapamil? | Authors/Editors* | Rossokhin A, Dreker T, Grissmer S, Zhorov BS. |
|---|---|
| Where published* | Molecular Pharmacology |
| How published* | Journal |
| Year* | 2011 |
| Volume | 79 |
| Number | 4 |
| Pages | 681-91 |
| Publisher | |
| Keywords | |
| Link | http://www.ncbi.nlm.nih.gov/pubmed/21220411 |
| Abstract |
hKv1.3 channels in lymphocytes are targets for the chemotherapy treatment of autoimmune diseases. Phenylalkylamines block Kv1.3 channels by poorly understood mechanisms. In the inactivation-reduced mutant H399T, the second mutation A413C in S6 substantially decreases the potency of phenylalkylamines with a para-methoxy group at the phenylethylamine end, whereas potency of phenylalkylamines lacking this group is less affected. Intriguingly, completely demethoxylated emopamil blocks mutant H399T/A413C with a 2:1 stoichiometry. Here, we generated a triple mutant, H399T/C412A/A413C, and found that its emopamil-binding properties are similar to those of the double mutant. These data rule out disulfide bonding Cys412-Cys413, which would substantially deform the inner helix, suggest a clash of Cys413 with the para-methoxy group, and provide a distance constraint to dock phenylalkylamines in a Kv1.2-based homology model. Monte Carlo minimizations predict that the verapamil ammonium group donates an H-bond to the backbone carbonyl of Thr391 at the P-loop turn, the pentanenitrilephenyl moiety occludes the pore, whereas the phenylethylamine meta- and para-methoxy substituents approach, respectively, the side chains of Met390 and Ala413. In the double-mutant model, the Cys413 side chains accept H-bonds from two emopamil molecules whose phenyl rings fit in the hydrophobic intersubunit interfaces, whereas the pentanenitrilephenyl moieties occlude the pore. Because these interfaces are unattractive for a methoxylated phenyl ring, the ammonium group of respective phenylalkylamines cannot approach the Cys413 side chain and binds at the focus of P-helices, whereas the para-methoxy group clashes with Cys413. Our study proposes an atomistic mechanism of Kv1.3 block by phenylalkylamines and highlights the intra- and intersubunit interfaces as ligand binding loci. |
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