Structural Properties of PAS Domains from the KCNH Potassium Channels

Abstract

KCNH channels form an important family of voltage gated potassium channels. These channels include a N-terminal Per-Arnt-Sim (PAS) domain with unknown function. In other proteins PAS domains are implicated in cellular responses to environmental queues through small molecule binding or involvement in signaling cascades. To better understand their role we characterized the structural properties of several channel PAS domains. We determined high resolution structures of PAS domains from the mouse EAG (mEAG), drosophila ELK (dELK) and human ERG (hERG) channels and also of the hERG domain without the first nine amino acids. We analyzed these structures for features connected to ligand binding and signaling in other PAS domains. In particular, we have found cavities in the hERG and mEAG structures that share similarities with the ligand binding sites from other PAS domains. These cavities are lined by polar and apolar chemical groups and display potential flexibility in their volume. We have also found that the hydrophobic patch on the domain β-sheet is a conserved feature and appears to drive the formation of protein-protein contacts. In addition, the structures of the dELK domain and of the truncated hERG domain revealed the presence of N-terminal helices. These helices are equivalent to the helix described in the hERG NMR structures and are known to be important for channel function. Overall, these channel domains retain many of the PAS domain characteristics known to be important for cell signaling.

Role of the Cytoplasmic N-terminal Cap and Per-Arnt-Sim (PAS) Domain in Trafficking and Stabilization of Kv11.1 Channels

“…Recent crystallography studies suggest that the N-Cap amphipathic helix of Kv11.1a can bind to a surface-exposed hydrophobic patch on the PAS domain (26). Accordingly, we hypothesized that the reduced thermostability and severely impaired trafficking of the N-Cap truncated constructs was a result of the PAS domain hydrophobic patch no longer being covered by the N-Cap amphipathic helix.…”

“…Structural models of the truncated PAS domain (residues 10 -135), based on the crystal structure from Adaixo et al (26), suggest that Leu-15, Ile-18, and Ile-19 would interact with this patch. We used a double mutant cycle approach to investigate whether L15S, I18S, and/or I19S had additive effects on the trafficking phenotype of the M124R mutant.…”

“…Subsequent NMR studies from a number of laboratories have shown that the N-Cap contains an amphipathic helix (N-Cap helix, residues 13-23) and a flexible * This work was supported by Grant-in-aid G11S 5829 from the Health Foun-N-terminal tail (N-tail, residues 1-12) (13)(14)(15). More recently, using a construct in which the flexible N-terminal tail was deleted, Morais-Cabral and co-workers (26) showed that the N-Cap helix can fold back and interact with a surface-exposed hydrophobic patch on the remainder of the PAS domain. In numerous previous studies, it had been suggested that the hydrophobic patch on the surface of the PAS domain was important for domain-domain interactions (9,16,17), and it had also been suggested that it may interact with the cNBH domain in the cytoplasmic C terminus (18).…”

Multiple Interactions between Cytoplasmic Domains Regulate Slow Deactivation of Kv11.1 Channels

“…That of Kv10.1-The PAS domains from Kv10.1 and Kv11.1 channels show remarkable similarity in both their amino acid sequence and in their atomic structures (19). However, the kinetics of channel deactivation are much slower in Kv11.1 channels than in Kv10.1 channels (20), suggesting that the N-Cap/PAS domain and cNBH domains form different functional interactions in these two channels.…”

“…A crystal structure complex of the PAS and cNBH domains from a closely related murine Kv10.1 channel provides the first atomic detail that these domains form a direct interaction (18). Interestingly the atomic structures of the PAS domain from the Kv10.1 and Kv11.1 channels are almost identical (19). However, the connection of the N-Cap domain to the PAS domain of these two channels appears to be different (18).…”