Subtype-selective positive modulation of K 2 channels depends on the HA/HB helices.

BACKGROUND AND PURPOSE

In the activated state of small-conductance Ca -activated potassium (K 2) channels, calmodulin interacts with the HA/HB helices and the S4-S5 linker. CyPPA potentiates K 2.2a and K 2.3 channel activity but not the K 2.1 and K 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 2 channels by CyPPA.

KEY RESULTS

Mutating residues in the HA (V420) and HB (K467) helices of K 2.2a channels to their equivalent residues in K 3.1 channels diminished the potency of CyPPA. CyPPA elicited prominent responses on mutant K 3.1 channels with an arginine residue in the HB helix substituted for its equivalent lysine residue in the K 2.2a channels (R355K). K 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 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 2.2a channels.

CONCLUSION AND IMPLICATIONS

Selectivity of CyPPA among K 2 and K 3.1 channel subtypes relies on the HA/HB helices.