title: A hydrophobicity-dependent motif responsible for surface expression of cardiac potassium channel.
abstract: The long-QT syndrome (LQTS) is an inherited cardiac disorder associated with syncope and a high risk of sudden death. The molecular basis of type-1 LQTS (LQT1) is a missense or nonsense mutation in KCNQ channels that reduces slowly activating delayed rectifier potassium channel (I(Ks)) resulting in a prolonged action potential. Noticeably, the S2-S3 linker is a highly congregating region of LQT1 mutations. To further explore the mechanism, a KCNQ mutant (L191P) identified in one Chinese pedigree with LQT1 was chosen for this purpose. As Leu-191 is located in the middle of a well-known endoplasmic reticulum (ER) localization signal (RXR) in the intracellular S2-S3 linker, we examined the kinetics and the surface expression of both the KCNQ1 and L191 mutants. Our results showed that the mutation did not affect the channel kinetics, whereas the surface expression increased with increasing hydrophobicity of the middle residue 'X' of the RXR motif. Based on an analysis of fractional fluorescence data using a binomial model, we also found that the percentage of KCNQ1/L191P heteromeric channels expressed at the cell surface were 22.0%, 40.5%, 27.9%, 8.6% and 1.0% of heteromeric channels with 0, 1, 2, 3 and 4 subunits of L191P, respectively, in a transfected ratio of KCNQ1: L191P=1:1. These experiments demonstrated that coexpression of L191P resulted in a trafficking factor alpha<1, causing a trafficking deficiency of heteromeric channels that underlay the dominant-negative effect. This study suggests several trafficking signals coexisting in this region, and expands our understanding of possible dominant-negative mechanisms underlying LQTS.
authors.affiliation: Key laboratory of Molecular Biophysics (Huazhong University of Science and Technology) of the Ministry of Education, Wuhan 430074, PR China.
authors.forename: Na
authors.initials: N
authors.lastname: Pan
authors.forename: Jing
authors.initials: J
authors.lastname: Sun
authors.forename: Caixia
authors.initials: C
authors.lastname: Lv
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.forename: Jiuping
authors.initials: J
authors.lastname: Ding
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002478:Cells, Cultured; D004594:Electrophysiology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D051657:KCNQ1 Potassium Channel / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008133:Long QT Syndrome / Q000235:genetics / Q000378:metabolism; D008164:Luminescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D014162:Transfection
chemical_list: D051657:KCNQ1 Potassium Channel; D008164:Luminescent Proteins