title: The binding site for channel blockers that rescue misprocessed human long QT syndrome type 2 ether-a-gogo-related gene (HERG) mutations.
abstract: Mutations in the human ether-a-gogo-related gene (HERG) K(+) channel gene cause chromosome 7-linked long QT syndrome type 2 (LQT2), which is characterized by a prolonged QT interval in the electrocardiogram and an increased susceptibility to life-threatening cardiac arrhythmias. LQT2 mutations produce loss-of-function phenotypes and reduce I(Kr) currents either by the heteromeric assembly of non- or malfunctioning channel subunits with wild type subunits at the cell surface or by retention of misprocessed mutant HERG channels in the endoplasmic reticulum. Misprocessed mutations often encode for channel proteins that are functional upon incorporation into the plasma membrane. As a result the pharmacological correction of folding defects and restoration of protein function are of considerable interest. Here we report that the trafficking-deficient pore mutation HERG G601S was rescued by a series of HERG channel blockers that increased cell surface expression. Rescue by these pharmacological chaperones varied directly with their blocking potency. We used structure-activity relationships and site-directed mutagenesis to define the binding site of the pharmacological chaperones. We found that binding occurred in the inner cavity and correlated with hydrophobicity and cationic charge. Rescue was domain-restricted because the trafficking of two misprocessed mutations in the C terminus, HERG F805C and HERG R823W, was not restored by channel blockers. Our findings represent a first step toward the design of pharmacological chaperones that will rescue HERG K(+) channels without block.
authors.affiliation: Rammelkamp Center for Education and Research, MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio 44109, USA. eficker@metrohealth.org
authors.forename: Eckhard
authors.initials: E
authors.lastname: Ficker
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Obejero-Paz
authors.forename: Shuxia
authors.initials: S
authors.lastname: Zhao
authors.forename: Arthur M
authors.initials: AM
authors.lastname: Brown
mesh_terms: D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D016589:Astemizole / Q000494:pharmacology; D001562:Benzimidazoles / Q000494:pharmacology; D001665:Binding Sites; D015153:Blotting, Western; D027682:Cation Transport Proteins; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D020117:Cisapride / Q000494:pharmacology; D004268:DNA-Binding Proteins; D004305:Dose-Response Relationship, Drug; D000072237:ERG1 Potassium Channel; D004594:Electrophysiology; D051638:Ether-A-Go-Go Potassium Channels; D005765:Gastrointestinal Agents / Q000494:pharmacology; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D006801:Humans; D020128:Inhibitory Concentration 50; D007477:Ions; D008133:Long QT Syndrome / Q000235:genetics* / Q000378:metabolism*; D008956:Models, Chemical; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D018408:Patch-Clamp Techniques; D010880:Piperidines / Q000494:pharmacology; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated; D017510:Protein Folding; D011725:Pyridines / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D011802:Quinidine / Q000494:pharmacology; D013329:Structure-Activity Relationship; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG
chemical_list: D000889:Anti-Arrhythmia Agents; D001562:Benzimidazoles; D027682:Cation Transport Proteins; D004268:DNA-Binding Proteins; C072312:ERG protein, human; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; D005765:Gastrointestinal Agents; D006634:Histamine H1 Antagonists; D007477:Ions; C000606913:KCNH2 protein, human; C092509:KCNH6 protein, human; D010880:Piperidines; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011725:Pyridines; D000644:Quaternary Ammonium Compounds; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; C063968:E 4031; D016589:Astemizole; D011802:Quinidine; D020117:Cisapride; C106448:tecastemizole