Hydrophobic interactions as key determinants to the KCa3.1 channel closed configuration. An analysis of KCa3.1 mutants constitutively active in zero Ca2+.
In this study we present evidence that residue Val282 in the S6 transmembrane segment of the calcium-activated KCa3.1 channel constitutes a key determinant of channel gating. A Gly scan of the S6 transmembrane segment first revealed that the substitutions A279G and V282G cause the channel to become constitutively active in zero Ca2+. Constitutive activity was not observed when residues extending from Cys276 to Ala286, other than Ala279 and Val282, were substituted to Gly. The accessibility of Cys engineered at Val275 deep in the channel cavity was next investigated for the ion-conducting V275C/V282G mutant and closed V275C channel in zero Ca2+ using Ag+ as probe. These experiments demonstrated that internal Ag+ ions have free access to the channel cavity independently of the channel conducting state, arguing against an activation gate located at the S6 segment C-terminal end. Experiments were also conducted where Val282 was substituted by residues differing in size and/or hydrophobicity. We found a strong correlation between constitutive activity in zero Ca2+ and the hydrophobic energy for side chain burial. Single channel recordings showed finally that constitutive activation in zero Ca2+ is better explained by a model where the channel is locked in a low conducting state with a high open probability rather than resulting from a change in the open/closed energy balance that would favor channel openings to a full conducting state in the absence of Ca2+. We conclude that hydrophobic interactions involving Val282 constitute key determinants to KCa3.1 gating by modulating the ion conducting state of the selectivity filter through an effect on the S6 transmembrane segment.
Garneau
Line
L
Dápartement de Physiologie, Groupe d'Étude sur les Protáines Membranaires, Facultá de Mádecine, Universitá de Montráal, Montráal, Quábec H3C 3J7, Canada.
Klein
Háléne
H
Dápartement de Physiologie, Groupe d'Étude sur les Protáines Membranaires, Facultá de Mádecine, Universitá de Montráal, Montráal, Quábec H3C 3J7, Canada.
Banderali
Umberto
U
Dápartement de Physiologie, Groupe d'Étude sur les Protáines Membranaires, Facultá de Mádecine, Universitá de Montráal, Montráal, Quábec H3C 3J7, Canada.
Longprá-Lauzon
Ariane
A
Dápartement de Physiologie, Groupe d'Étude sur les Protáines Membranaires, Facultá de Mádecine, Universitá de Montráal, Montráal, Quábec H3C 3J7, Canada.
Parent
Lucie
L
Dápartement de Physiologie, Groupe d'Étude sur les Protáines Membranaires, Facultá de Mádecine, Universitá de Montráal, Montráal, Quábec H3C 3J7, Canada.
Sauvá
Rámy
R
Dápartement de Physiologie, Groupe d'Étude sur les Protáines Membranaires, Facultá de Mádecine, Universitá de Montráal, Montráal, Quábec H3C 3J7, Canada. Electronic address: remy.sauve@umontreal.ca.
D019943:Amino Acid Substitution; D000818:Animals; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015640:Ion Channel Gating / Q000502:physiology*; D017136:Ion Transport / Q000502:physiology; D008958:Models, Molecular; D020125:Mutation, Missense; D017433:Protein Structure, Secondary / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D012834:Silver / Q000737:chemistry* / Q000378:metabolism
D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496923:KCNN4 protein, human; D012834:Silver; D002118:Calcium