The NH2 Terminus of RCK1 Domain Regulates Ca2+-dependent BKCa Channel Gating

Abstract

Large conductance, voltage- and Ca2+-activated K+ (BKCa) channels regulate blood vessel tone, synaptic transmission, and hearing owing to dual activation by membrane depolarization and intracellular Ca2+. Similar to an archeon Ca2+-activated K+ channel, MthK, each of four α subunits of BKCa may contain two cytosolic RCK domains and eight of which may form a gating ring. The structure of the MthK channel suggests that the RCK domains reorient with one another upon Ca2+ binding to change the gating ring conformation and open the activation gate. Here we report that the conformational changes of the NH2 terminus of RCK1 (AC region) modulate BKCa gating. Such modulation depends on Ca2+ occupancy and activation states, but is not directly related to the Ca2+ binding sites. These results demonstrate that AC region is important in the allosteric coupling between Ca2+ binding and channel opening. Thus, the conformational changes of the AC region within each RCK domain is likely to be an important step in addition to the reorientation of RCK domains leading to the opening of the BKCa activation gate. Our observations are consistent with a mechanism for Ca2+-dependent activation of BKCa channels such that the AC region inhibits channel activation when the channel is at the closed state in the absence of Ca2+; Ca2+ binding and depolarization relieve this inhibition.

Presynaptic Ca2+/Calmodulin-Dependent Protein Kinase II Modulates Neurotransmitter Release by Activating BK Channels atCaenorhabditis elegansNeuromuscular Junction

“…The fact that T 425 A mutation abolished SLO-1 activation by CaMKII in Xenopus oocytes suggests that UNC-43 likely activates SLO-1 by directly phosphorylating the channel protein. This putative CaMKII phosphorylation site is located in the first RCK domain of the BK channel, which plays key roles in Ca 2ϩ -dependent channel gating (Jiang et al, 2001(Jiang et al, , 2002Krishnamoorthy et al, 2005;Santarelli et al, 2006). Interestingly, T 425 is only three residues upstream of a conserved glutamate residue (E 399 in mSlo, the mouse BK channel), which, when mutated to alanine, increases mSlo V 50 at nonphysiologically high Ca 2ϩ concentrations (Ն1 mM) (Xia et al, 2002).…”

A Novel Actin-Binding Domain on Slo1 Calcium-Activated Potassium Channels Is Necessary for Their Expression in the Plasma Membrane

“…We are experimentally limited by the fact that complete inhibition of actin binding seems to prevent surface expression, which precludes making the necessary recordings. However, it is worth noting that the ABD in Slo1 channels is located considerably downstream of the regulator of conductance of K ϩ channels domain and calcium bowl domain that are thought to comprise the Ca 2ϩ -binding sites that mediate most physiological gating processes of these channels (Krishnamoorthy et al, 2005;Zeng et al, 2005). The ABD is also located at some distance from a pair of noncanonical C-terminal Src homology 3 domains that are involved in stretch-sensitive gating (Tian et al, 2006).…”

“…Moreover, Slo1 channels can coimmunoprecipitate with actin (Brainard et al, 2005), and the cytosolic domains in Slo1 can bind to cortactin, an actin-binding scaffolding protein (Tian et al, 2006). This latter interaction seems to be essential for stretch-induced activation of BK Ca channels, and it occurs in a cytosolic region of the channel close to a domain known to play a role in Ca 2ϩ -dependent gating (Krishnamoorthy et al, 2005;Zeng et al, 2005;Tian et al, 2006).…”

Modulation of MthK Potassium Channel Activity at the Intracellular Entrance to the Pore

“…Each MthK RCK domain contains a Ca 2ϩ -binding site. By sequence comparison and alignment, at least one apparent RCK-like domain can be found within the large cytoplasmic tail region of the mammalian maxi-K channel, and consequently MthK has served as a model to provide insight toward maxi-K channel structure and gating mechanism (1,2,4,5).…”