title: Probing the outer mouth structure of the HERG channel with peptide toxin footprinting and molecular modeling.
abstract: Previous studies have shown that the unusually long S5-P linker lining human ether a-go-go related gene's (hERG's) outer vestibule is critical for its channel function: point mutations at high-impact positions here can interfere with the inactivation process and, in many cases, also reduce the pore's K+ selectivity. Because no data are available on the equivalent region in the available K channel crystal structures to allow for homology modeling, we used alternative approaches to model its three-dimensional structure. The first part of this article describes mutant cycle analysis used to identify residues on hERG's outer vestibule that interact with specific residues on the interaction surface of BeKm-1, a peptide toxin with known NMR structure and a high binding affinity to hERG. The second part describes molecular modeling of hERG's pore domain. The transmembrane region was modeled after the crystal structure of KvAP pore domain. The S5-P linker was docked to the transmembrane region based on data from previous NMR and mutagenesis experiments, as well as a set of modeling criteria. The models were further restrained by contact points between hERG's outer vestibule and the bound BeKm-1 toxin molecule deduced from the mutant cycle analysis. Based on these analyses, we propose a working model for the open conformation of the outer vestibule of the hERG channel, in which the S5-P linkers interact with the pore loops to influence ion flux through the pore.
authors.affiliation: Department of Physiology, Virginia Commonwealth University, Richmond, Virginia 23298, USA. gtseng@vcu.edu
authors.forename: Gea-Ny
authors.initials: GN
authors.lastname: Tseng
authors.forename: Kailas D
authors.initials: KD
authors.lastname: Sonawane
authors.forename: Yuliya V
authors.initials: YV
authors.lastname: Korolkova
authors.forename: Mei
authors.initials: M
authors.lastname: Zhang
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.forename: Eugene V
authors.initials: EV
authors.lastname: Grishin
authors.forename: H Robert
authors.initials: HR
authors.lastname: Guy
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D002478:Cells, Cultured; D003198:Computer Simulation; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D015640:Ion Channel Gating / Q000502:physiology*; D008954:Models, Biological; D008956:Models, Chemical; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000502:physiology; D010449:Peptide Mapping / Q000379:methods; D012604:Scorpion Venoms / Q000737:chemistry* / Q000378:metabolism*; D020539:Sequence Analysis, Protein; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
chemical_list: C425305:BeKm-1 toxin; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D012604:Scorpion Venoms