Putative alpha-1,2-glucosyltransferase, which adds the third glucose residue to the lipid-linked oligosaccharide precursor for N-linked glycosylation. Transfers glucose from dolichyl phosphate glucose (Dol-P-Glc) onto the lipid-linked oligosaccharide Glc(2)Man(9)GlcNAc(2)-PP-Dol. When coupled to KCNH2 may reduce KCNH2 sensitivity to classic proarrhythmic drug blockade, possibly by mediating glycosylation of KCNH2.
Human ether-a-go-go-related gene (HERG) encodes the pore-forming subunit of I(Kr), a cardiac K(+) channel. Although many commonly used drugs block I(Kr), in certain individuals, this action evokes a paradoxical life-threatening cardiac rhythm disturbance, known as the acquired long QT syndrome (aLQTS). Although aLQTS has become the leading cause of drug withdrawal by the U.S. Food and Drug Administration, DNA sequencing in aLQTS patients has revealed HERG mutations only in rare cases, suggesting that unknown HERG modulators are often responsible. By using the worm Caenorhabditis elegans, we have developed in vivo behavioral assays that identify candidate modulators of unc-103, the worm HERG orthologue. By using RNA-interference methods, we have shown that worm homologues of two HERG-interacting proteins, Hyperkinetic and K channel regulator 1 (KCR1), modify unc-103 function. Examination of the human KCR1 sequence in patients with drug-induced cardiac repolarization defects revealed a sequence variation (the substitution of isoleucine 447 by valine, I447V) that occurs at a reduced frequency (1.1%) relative to a matched control population (7.0%), suggesting that I447V may be an allele for reduced aLQTS susceptibility. This clinical result is supported by in vitro studies of HERG dofetilide sensitivity by using coexpression of HERG with wild-type and I447V KCR1 cDNAs. Our studies demonstrate the feasibility of using C. elegans to assay and potentially identify aLQTS candidate genes.
The cardiac potassium channel encoded by the human ether-à-go-go related gene (HERG) is blocked by a diverse array of common therapeutic compounds. Even transient exposure to such agents may provoke the life-threatening cardiac arrhythmia torsades de pointes in some, but not all, individuals. Although the molecular and genetic factors predicting such wide variability in drug response remain unclear, known sequence variations within the coding region of HERG do not explain the adverse drug response in many cases. Although other proteins can modulate HERG function, no studies have identified protein partners capable of limiting the pharmacological sensitivity of HERG. Here we show that KCR1, a protein identified previously in rat cerebellum, is a plasma membrane-associated protein expressed at the RNA level in the human heart and can be immunoprecipitated with HERG. Functionally, KCR1 reduces the sensitivity of HERG to classic proarrhythmic HERG blockers (sotalol, quinidine, dofetilide) in both cardiac and noncardiac cell lines. We propose that KCR1, when coupled to HERG, may limit the sensitivity of HERG to proarrhythmic drug blockade and may be a rational target for modifying the proarrhythmic effects of otherwise clinically useful compounds.
Human ether-a-go-go-related gene (HERG) encodes the pore-forming subunit of I(Kr), a cardiac K(+) channel. Although many commonly used drugs block I(Kr), in certain individuals, this action evokes a paradoxical life-threatening cardiac rhythm disturbance, known as the acquired long QT syndrome (aLQTS). Although aLQTS has become the leading cause of drug withdrawal by the U.S. Food and Drug Administration, DNA sequencing in aLQTS patients has revealed HERG mutations only in rare cases, suggesting that unknown HERG modulators are often responsible. By using the worm Caenorhabditis elegans, we have developed in vivo behavioral assays that identify candidate modulators of unc-103, the worm HERG orthologue. By using RNA-interference methods, we have shown that worm homologues of two HERG-interacting proteins, Hyperkinetic and K channel regulator 1 (KCR1), modify unc-103 function. Examination of the human KCR1 sequence in patients with drug-induced cardiac repolarization defects revealed a sequence variation (the substitution of isoleucine 447 by valine, I447V) that occurs at a reduced frequency (1.1%) relative to a matched control population (7.0%), suggesting that I447V may be an allele for reduced aLQTS susceptibility. This clinical result is supported by in vitro studies of HERG dofetilide sensitivity by using coexpression of HERG with wild-type and I447V KCR1 cDNAs. Our studies demonstrate the feasibility of using C. elegans to assay and potentially identify aLQTS candidate genes.
Enzymes that catalyze the transfer of glycosyl (sugar) residues to an acceptor, both during degradation (cosubstrates= water or inorganic phosphate) and during biosynthesis of polysaccharides, glycoproteins and glycolipids. In biosynthetic glycosyl transfers, the common activated monomeric sugar intermediate is a nucleoside diphosphate sugar.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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