The interface between membrane-spanning and cytosolic domains in Ca2+-dependent K+ channels is involved in β subunit modulation of gating

Abstract

Large-conductance, voltage-, and Ca2+-dependent K+ (BK) channels are broadly expressed in various tissues to modulate neuronal activity, smooth muscle contraction, and secretion.BKchannel activation depends on the interactions among the voltage sensing domain (VSD), the cytosolic domain (CTD), and the pore gate domain (PGD) of the Slo1 α-subunit, and is further regulated by accessory β subunits (β1-β4). Howβ subunits fine-tune BK channel activation is critical to understand the tissue-specific functions of BK channels. Multiple sites in both Slo1 and the β subunits have been identified to contribute to the interaction between Slo1 and the β subunits. However, it is unclear whether andhowthe interdomain interactionsamongthe VSD, CTD, andPGDare altered by theβ subunits to affect channel activation. Here we show that human β1 and β2 subunits alter interactions between bound Mg2+ and gating charge R213 and disrupt the disulfide bond formation at theVSD-CTDinterface ofmouseSlo1, indicating that theβ subunits alter theVSD-CTDinterface. Reciprocally, mutations in the Slo1 that alter the VSD-CTD interaction can specifically change the effects of theβ1 subunit on the Ca2+ activation and of the β2 subunit on the voltage activation. Together, our data suggest a novel mechanism by which the β subunits modulatedBKchannel activation such that aβ subunitmayinteract with theVSDor theCTDand alter theVSD-CTDinterface of the Slo1, which enables the β subunit to have effects broadly on both voltage and Ca2+-dependent activation. © 2013 Asian Network for Scientific Information.