Effects of the Accessory Subunit γ1 on the External Architecture of BK Channel

Abstract

Regulatory β and γ subunits are responsible for conferring functional diversity to BK channels but little is known about the detailed way that accessory subunits modulate the structure of the pore forming α subunit. It is known that the γ1 subunit produces a large leftward shift of the open probability vs. voltage curve in the absence of internal Ca2+ (Yan and Aldrich, 2010). To explore the external architecture of α subunit in the presence of γ1 subunit, we used lanthanide-based resonance energy transfer (LRET) as a molecular ruler to measure intra- and inter-molecular distances. We introduced a genetically encoded lanthanide binding tag (LBT) that binds Tb3+ (LRET donor) with high affinity at different positions in the α subunit (N-terminal, S0, S1 and S2) and γ1 subunit. Fluorescent probe BODIPY linked to a scorpion toxin was used as LRET acceptor. LRET sensitized emission (SE) decays were analysed using a nano-positioning system that determines the position of LBT-tagged sites with respect to the fixed acceptor near the pore axis. Interestingly, the external architecture of the BK α subunit is modified when co-expressed with the regulatory γ1 subunit indicating a conformational change of the BK voltage sensor domain of the BK channel. The largest changes was in S1 position (∼25 Angstroms) followed by S0. In addition, all γ1-LBT positions were found peripherally positioned with respect to the α subunit.Fondecyt Grant 1110430 (To R. L.)