Cryo-EM structure of the open high-conductance Ca2+-activated K+ channel

Abstract

The Ca2+-activated K+ channel, Slo1, has an unusually large conductance and contains a voltage sensor and multiple chemical sensors. Dual activation by voltage and Ca2+ renders Slo1 central to numerous cellular processes that couple electrical signaling to Ca2+-mediated events such as muscle contraction and neuronal excitability. Here we present the cryo-electron microscopy structure of a full-length Slo1 channel from Aplysia californica in the presence of Ca2+ and Mg2+ at a resolution of 3.5 Å. The channel adopts an open conformation. Its voltage sensor domain adopts a non-domain-swapped attachment to the pore and contacts the cytoplasmic Ca2+-binding domain from a neighboring subunit. Unique structural features of the Slo1 voltage sensor suggest that Slo1 likely employs a voltage sensing mechanism quite distinct from known voltage-dependent ion channels. The structure reveals the molecular details of three distinct divalent cation-binding sites identified through electrophysiological studies of mutant Slo1 channels.

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).…”

Activation mechanism of a human SK-calmodulin channel complex elucidated by cryo-EM structures

“…1C). This arrangement is similar to that of the BK channel (also known as Slo1) but different from that of domain-swapped K v 1 to K v 7 channels, where helices S1 to S4 interact with a neighboring pore domain (18, 24, 25). …”

Structure of the cold- and menthol-sensing ion channel TRPM8

“…The lack of a bending point in S5 calls to question whether TRPM8 FA possesses an S4–S5 linker, which is the structural element critical for vanilloid-dependent TRPV1 gating (26); however, it is possible that a transition from α to π helix in the TRPM8 FA S5 may occur during gating, as was suggested for TRPV2 (23). Despite the absence of an obvious S4–S5 linker, TRPM8 FA nonetheless forms a domain-swapped tetramer, which is in stark contrast to the calcium-activated K + channel Slo1, where a similarly short S4–S5 linker prevents formation of a domain-swapped tetramer (27). The overlay of TRPM8 FA and TRPV1 protomers reveals that the C-terminal part of TRPM8 FA S4 is longer and straight such that it can connect with S5 to achieve a domain-swapped configuration.…”