Relationship between auxiliary gamma subunits and mallotoxin on BK channel modulation.
The large-conductance, calcium- and voltage-activated K+(BK) channel consists of the pore-forming α subunits (BKα) and auxiliary subunits. The auxiliary γ1-3 subunits potently modulate the BK channel by shifting its voltage-dependence of channel activation toward the hyperpolarizing direction by approximately 145 mV (γ1), 100 mV (γ2), and 50 mV (γ3). Mallotoxin is a potent small-molecule BK channel activator. We analyzed the relationship between mallotoxin and the γ subunits in their BK channel-activating effects in membrane patches excised from HEK-293 cells. We found that mallotoxin, when applied extracellularly, shifted the half-activation voltage (V1/2) of BKα channels by -72 mV. The channel-activating effect of mallotoxin was greatly attenuated in the presence of the γ1, γ2, or γ3 subunit, with resultant ΔV1/2 (+/- mallotoxin)values of -9, -28, or -15 mV, respectively. Most examined γ1 mutant subunits antagonized mallotoxin's channel-activating effect in a manner that was largely dependent on its own modulatory function. However, mallotoxin caused an irreversible functional and structural disengagement of the γ1-F273S mutant from BK channels. We infer that the auxiliary γ subunit effectively interferes with mallotoxin on BK channel modulation via either a direct steric competition or an indirect allosteric influence on mallotoxin's binding and action on BKα.
Department of Anesthesiology and Perioperative Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
Xin
X
Guan
Department of Anesthesiology and Perioperative Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
Qin
Q
Li
Department of Anesthesiology and Perioperative Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
Jiusheng
J
Yan
D000098:Acetophenones / Q000633:toxicity*; D000595:Amino Acid Sequence; D001578:Benzopyrans / Q000633:toxicity*; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects*; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D000098:Acetophenones; D001578:Benzopyrans; D051036:Large-Conductance Calcium-Activated Potassium Channels; D021122:Protein Subunits; C085746:rottlerin