Structural Determinants for the Selectivity of the Positive KCa3.1 Gating Modulator 5-Methylnaphtho[2,1-d]oxazol-2-amine (SKA-121).

摘要: Intermediate-conductance (KCa3.1) and small-conductance (KCa2) calcium-activated K+ channels are gated by calcium binding to calmodulin (CaM) molecules associated with the calmodulin-binding domain (CaM-BD) of these channels. The existing KCa activators, such as naphtho[1,2-d]thiazol-2-ylamine (SKA-31), 6,7-dichloro-1H-indole-2,3-dione 3-oxime (NS309), 1-ethylbenzimidazolin-2-one (EBIO), activate both channel types similar potencies. In a previous chemistry effort, we optimized benzothiazole pharmacophore SKA-31 toward KCa3.1 selectivity identified 5-methylnaphtho[2,1-d]oxazol-2-amine (SKA-121), which exhibits 40-fold for over KCa2.3. To understand why introduction single CH3 group in five-position benzothiazole/oxazole system could achieve gain KCa2.3, first localized site benzothiazoles/oxazoles CaM-BD/CaM interface then used computational modeling software generate models KCa2.3 complexes SKA-121. Based on combination mutagenesis structural modeling, suggest that all benzothiazole/oxazole-type activators bind relatively “deep” hydrogen bond E54 CaM. KCa3.1, SKA-121 forms an additional network R362. contrast, NS309 sits more “forward” directly bonds R362 KCa3.1. Mutating serine, corresponding residue reduces potency 7-fold, suggesting is responsible generally greater increase SKA-121’s compared its parent, SKA-31, seems be due better overall shape complementarity hydrophobic interactions S372 M368 M72 CaM at KCa3.1–CaM-BD/CaM interface.