Background and Purpose
In the activated state of small-conductance Ca2+-activated potassium (KCa 2) channels, calmodulin interacts with the HA/HB helices and the S4-S5 linker. CyPPA potentiates KCa 2.2a and KCa 2.3 channel activity but not the KCa 2.1 and KCa 3.1 subtypes.
Site-directed mutagenesis, patch-clamp recordings and in silico modeling were utilized to explore the structural determinants for the subtype-selective modulation of KCa 2 channels by CyPPA.
Mutating residues in the HA (V420) and HB (K467) helices of KCa 2.2a channels to their equivalent residues in KCa 3.1 channels diminished the potency of CyPPA. CyPPA elicited prominent responses on mutant KCa 3.1 channels with an arginine residue in the HB helix substituted for its equivalent lysine residue in the KCa 2.2a channels (R355K). KCa 2.1 channels harboring a three-amino-acid insertion upstream of the cognate R438 residues in the HB helix showed no response to CyPPA, whereas the deletion mutant (KCa 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 KCa 2.2a channels.
Conclusion and Implications
Selectivity of CyPPA among KCa 2 and KCa 3.1 channel subtypes relies on the HA/HB helices.
Nam, Y-W, Cui, M, Salem, N, et al. Subtype-selective positive modulation of KCa 2 channels depends on the HA/HB helices. Br J Pharmacol. 2021;179(3):460-472. https://doi.org/10.1111/bph.15676
British Pharmacological Society