Structural basis for gating the high-conductance Ca2+-activated K+ channel

Abstract

The precise control of an ion channel’s gate by environmental stimuli is crucial to the fulfillment of its biological role. The gate in Slo1 channels is regulated by two separate stimuli, intracellular Ca2+ concentration and membrane voltage. Thus, Slo1 is central to understanding the relationship between intracellular Ca2+ and membrane excitability. Here we present the Slo1 structure in the absence of Ca2+ and compare it with the Ca2+-bound channel. Ca2+ binding at two unique binding sites per subunit stabilizes an expanded conformation of the Ca2+ sensor gating ring. These conformational changes are propagated from the gating ring to the pore through covalent linkers and through protein interfaces formed between the gating ring and the voltage sensors. The gating ring and voltage sensors are directly connected through these interfaces, which allow membrane voltage to regulate gating of the pore by influencing the Ca2+ sensors.

Structural Titration of Slo2.2, a Na + -Dependent K + Channel

“…Expansion of RCK1 N-lobes induced by Na + is similar to the expansion documented in the Slo1 Ca 2+ - and voltage-activated K + channel induced by Ca 2+ (Wu et al, 2010; Yuan et al, 2012; Tao et al, 2016; Hite et al, 2016). The concomitant changes in the S1–S4 voltage-sensing domains observed in Slo1, however, are not observed in Slo2.2.…”

The S1 helix critically regulates the finely tuned gating of Kv11.1 channels

“…This segment is postulated to play a role in biogenesis, protein folding, and gating of these channels (37)(38)(39)(40)(41)(42)(43)(44)(45). Our NMR spectroscopy and Gd 3ϩ suppression data did not support the presence of a pre-S1 helix in Kv11.1 channels.…”

“…The NMR data suggest that the transmembrane extent of S1 in Kv11.1 extends at least from Trp-410 to Leu-432, with a possible break or kink at Thr-425/Pro-426. The NMR data do not support a pre-S1 helical segment in Kv11.1 channels, a feature that is present in the structure of other voltage-gated ion channels (37)(38)(39)(40)(41)(42)(43) but not in the cryo-electron microscopy (cryo-EM) structure of rEAG (50).…”

“…A short intracellular helical segment located just prior to the transmembrane S1 helix has been observed in recent protein structures of a range of Kv channels, such as the Kv1.2/2.1 chimera (37), Slo2.2 (38), and K Ca 1.1 (also termed BK (39,40)), as well as various TRP channels, including TRPV channels (41)(42)(43) and TRPA1 channels (44). Termed the pre-S1, S0, or S0Ј helix, this short helical segment may play a role in the biogenesis, protein-folding, and inter-subunit interactions of TRPV channels (45).…”

Mechanistic insight into the heme-independent interplay between iron and carbon monoxide in CFTR and Slo1 BKCa channels

“…A coupling of electrical signaling to Ca 2+ -mediated events allows this channel to regulate muscle contraction, hormone secretion and neuronal excitability 50–51 . Recent Mg 2+ /Ca 2+ -free and Mg 2+ /Ca 2+ -bound cryo-EM structures of the full-length Slo1 channel from Aplysia californica demonstrated that the BK Ca channel is a tetramer with the transmembrane domain (TMD) on top, the first regulator of K + conductance (RCK1) domain in the middle and the RCK2 domain at the bottom (Figure 2) 52–53 . The TMD includes S0 helix, a voltage-sensor domain (VSD) with S1–S4 helices and a pore domain (PD) with S5–S6 helices.…”