马丽娟
云南省阜外心血管病医院
We have found a novel nonsense mutation in the C-terminus of HERG in a four-generation Chinese family with long QT syndrome and investigated the molecular mechanism of this mutation in vitro. Six family members, including the proband, were clinically affected. Syncope and ventricular tachycardia of torsades de pointes were triggered by startling or emotional stress, and beta-adrenergic blockade treatment was ineffective. Haplotype analysis showed that only LQT2 markers cosegregated with the disease, and sequence analysis revealed a substitution of T with C at nucleotide position 2770 of the HERG gene (U04270), which creates a stop codon at amino acid position 863 (R863X) of the HERG protein, leading to a deletion of 296 amino acids. Whole cell patch clamp studies showed that the R863X HERG could not induce time-dependent current. Coexpression of R863X with wild-type HERG showed reduced current densities and accelerated voltage-dependent inactivation of HERG channels. Subcellular localization of R863X-EGFP revealed that the mutant did not traffic to the cell surface. These data suggest that R863X failed to form functional HERG channels, contributing to a prolongation of the QT interval and long QT syndrome with a dominant phenotype. These findings provide new insights into the structure-function relationships of the HERG C-terminus.
Journal of molecular medicine (Berlin, Germany) 2004
OBJECTIVES:To identify the underlying genetic basis of a Chinese pedigree with Long QT syndrome, the causally related genes were screened in a family and the functional consequence of the identified gene mutation was evaluated in vitro.METHODS:Mutations in the five defined Long QT syndrome related genes were screened with polymerase chain reaction and single-strand conformation polymorphism methods and direct sequencing. The electrophysiological properties of the identified mutation were characterized in the Xenopus oocyte heterologous expression system.RESULTS:A novel missense mutation, G to A at position 154 in the KCNE1 gene was identified in a Chinese Long QT syndrome family, which leads to an amino acid substitution of arginine (R) for glycine (G) at position 52 (G52R-KCNE1). Of 26 family members (one DNA was not available), seven were mutation carriers and two of them with normal electrocardiogram. Compared with wild-type KCNE1/KCNQ1 channels, coexpression of G52R-KCNE1 with KCNQ1 in Xenopus oocytes did not amplify the KCNQ1 current amplitudes and slightly changed the activation kinetics of the KCNQ1 channels. Coexpression of KCNQ1 together with wild type KCNE1 and G52R-KCNE1 reduced the wild-type I(ks) current amplitude by 50%, whereas other biophysical properties of the I(ks) were not altered.CONCLUSIONS:Our findings indicate that glycine52 in the transmembrane domain is critical for KCNE1 function. The mutant G52R-KCNE1 has a dominant negative effect on I(ks) current, which reduces the I(ks) current amplitude and leads to a prolongation of the cardiac action potential. This could underlie the molecular mechanism of ventricular arrhythmias and sudden death in those patients.
Cardiovascular research 2003
The KCNE genes encode small, single transmembrane domain peptides that associate with pore-forming potassium channel subunits to form mixed complexes with unique characteristics. We have identified a novel member of the human KCNE gene family, hKCNE4. The hKCNE4 gene encodes 170 amino acid protein and is localized to chromosome 2q35-36. The protein sequence shows 90% homology to mouse KCNE4 and 38% identity to human KCNE1. Northern blot analysis revealed that hKCNE4 is expressed strongly in heart, skeletal muscle, and kidney, less in placenta, lung, and liver, and weakly in brain and blood cells. Electrophysiological study showed that hKCNE4 modulates the activation of the KCNQ1 channel.
Biochemical and biophysical research communications 2003
