Two classes of regulatory subunits coassemble in the same BK channel and independently regulate gating

High resolution proteomics increasingly reveals that most native ion channels are assembled in macromolecular complexes. However, whether different partners have additive or cooperative functional effects, or whether some combinations of proteins may preclude assembly of others are largely unexplored topics. The large conductance Ca2+-and-voltage activated potassium channel (BK) is well-suited to discern nuanced differences in regulation arising from combinations of subunits. Here we examine whether assembly of two different classes of regulatory proteins, β and γ, in BK channels is exclusive or independent. Our results show that both γ1 and up to four β2-subunits can coexist in the same functional BK complex, with the gating shift caused by β2-subunits largely additive with that produced by the γ1-subunit(s). The multiplicity of β:γ combinations that can participate in a BK complex therefore allow a range of BK channels with distinct functional properties tuned by the specific stoichiometry of the contributing subunits.