Role of the electrostatic potential on the BK potassium channel conductance

Abstract

The family of K channels presents a highly conserved structural motif (TVGYG), known as the selectivity filter. Despite the fact that the selectivity filter is conserved in all K channels, they show different conductances. We observed that the number of negative charged aminoacids in the outer vestibule of BK (high conductance), KvAP (medium conductance) and Shaker (low conductance) K channels, is proportional to the conductance of each channel. In particular, BK channel has a loop bearing two charged aminoacids in the outer vestibule. These negative charges would increase the local K ion concentration in the outer vestibule of the pore, diminishing the required energy to access the selectivity filter. To verify experimentally this hypothesis a series of BK channel mutants were constructed and the single channel conductances were measured. In agreement with our predictions, the removal of the loop charges (D261N/E264Q) leads to a reduced inward conductance. Deleting the outer loop does not affect inward conductance unless another charge is removed (Δloop/E276Q). This suggests that E276 can compensate the electrostatic contribution of the loop charges when the loop is deleted. The results are in agreement with electrostatic potential calculations (Poisson-Boltzmann) carried out on a molecular model of the BK channel pore. In conclusion, we have identified residues involved in the electrostatic tuning of the BK channel inward conductance. Acknowledgment: FONDECYT 1040254 (FG) and 1030830 (RL). Fundación Andes (FG)