Determination of the Stoichiometry between α- and γ1 Subunits of the BK Channel Using LRET

Abstract Two families of accessory proteins, β and γ , modulate BK channel gating and pharmacology. Notably, in the absence of internal Ca 2+ , the γ 1 subunit promotes a large shift of the BK conductance-voltage curve to more negative potentials. However, very little is known about how α - and γ 1 subunits interact. In particular, the association stoichiometry between both subunits is unknown. Here, we propose a method to answer this question using lanthanide resonance energy transfer. The method assumes that the kinetics of lanthanide resonance energy transfer-sensitized emission of the donor double-labeled α / γ 1 complex is the linear combination of the kinetics of the sensitized emission in single-labeled complexes. We used a lanthanide binding tag engineered either into the α - or the γ 1 subunits to bind Tb +3 as the donor. The acceptor (BODIPY) was attached to the BK pore-blocker iberiotoxin. We determined that γ 1 associates with the α -subunit with a maximal 1:1 stoichiometry. This method could be applied to determine the stoichiometry of association between proteins within heteromultimeric complexes.