Subtype‐selective positive modulation of K Ca 2 channels depends on the HA/HB helices

Background and Purpose In the activated state of small‐conductance Ca 2+ ‐activated potassium (K Ca 2) channels, calmodulin interacts with the HA/HB helices and the S4‐S5 linker. CyPPA potentiates K Ca 2.2a and K Ca 2.3 channel activity but not the K Ca 2.1 and K Ca 3.1 subtypes. Experimental Approach Site‐directed mutagenesis, patch‐clamp recordings and in silico modelling were utilised to explore the structural determinants for the subtype‐selective modulation of K Ca 2 channels by CyPPA. Key Results Mutating residues in the HA (V420) and HB (K467) helices of K Ca 2.2a channels to their equivalent residues in K Ca 3.1 channels diminished the potency of CyPPA. CyPPA elicited prominent responses on mutant K Ca 3.1 channels with an arginine residue in the HB helix substituted for its equivalent lysine residue in the K Ca 2.2a channels (R355K). K Ca 2.1 channels harbouring a three‐amino‐acid insertion upstream of the cognate R438 residues in the HB helix showed no response to CyPPA, whereas the deletion mutant (K Ca 2.1_ΔA434/Q435/K436) became sensitive to CyPPA. In molecular dynamics simulations, CyPPA docked between calmodulin C‐lobe and the HA/HB helices widens the cytoplasmic gate of K Ca 2.2a channels. Conclusion and Implications Selectivity of CyPPA among K Ca 2 and K Ca 3.1 channel subtypes relies on the HA/HB helices.