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Hydrophobic interactions between the HA helix and S4‐S5 linker modulate apparent Ca 2+ sensitivity of SK2 channels
Author(s) -
Nam YoungWoo,
Cui Meng,
Orfali Razan,
Viegas Adam,
Nguyen Misa,
Mohammed Eman H. M.,
Zoghebi Khalid A.,
Rahighi Simin,
Parang Keykavous,
Zhang Miao
Publication year - 2021
Publication title -
acta physiologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.591
H-Index - 116
eISSN - 1748-1716
pISSN - 1748-1708
DOI - 10.1111/apha.13552
Subject(s) - linker , chemistry , biophysics , helix (gastropod) , allosteric regulation , conductance , mutant , potassium channel , stereochemistry , mutagenesis , crystallography , biochemistry , biology , receptor , physics , ecology , snail , computer science , gene , condensed matter physics , operating system
Aim Small‐conductance Ca 2+ ‐activated potassium (SK) channels are activated exclusively by increases in intracellular Ca 2+ that binds to calmodulin constitutively associated with the channel. Wild‐type SK2 channels are activated by Ca 2+ with an EC 50 value of ~0.3 μmol/L. Here, we investigate hydrophobic interactions between the HA helix and the S4‐S5 linker as a major determinant of channel apparent Ca 2+ sensitivity. Methods Site‐directed mutagenesis, electrophysiological recordings and molecular dynamic (MD) simulations were utilized. Results Mutations that decrease hydrophobicity at the HA‐S4‐S5 interface lead to Ca 2+ hyposensitivity of SK2 channels. Mutations that increase hydrophobicity result in hypersensitivity to Ca 2+ . The Ca 2+ hypersensitivity of the V407F mutant relies on the interaction of the cognate phenylalanine with the S4‐S5 linker in the SK2 channel. Replacing the S4‐S5 linker of the SK2 channel with the S4‐S5 linker of the SK4 channel results in loss of the hypersensitivity caused by V407F. This difference between the S4‐S5 linkers of SK2 and SK4 channels can be partially attributed to I295 equivalent to a valine in the SK4 channel. A N293A mutation in the S4‐S5 linker also increases hydrophobicity at the HA‐S4‐S5 interface and elevates the channel apparent Ca 2+ sensitivity. The double N293A/V407F mutations generate a highly Ca 2+ sensitive channel, with an EC 50 of 0.02 μmol/L. The MD simulations of this double‐mutant channel revealed a larger channel cytoplasmic gate. Conclusion The electrophysiological data and MD simulations collectively suggest a crucial role of the interactions between the HA helix and S4‐S5 linker in the apparent Ca 2+ sensitivity of SK2 channels.