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The dominant negative LQT2 mutation A561V reduces wild-type HERG expression.
1Section of Molecular Cardiology, Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
The Journal of Biological Chemistry
|February 7, 2001
Summary
Mutations in the HERG(1) K(+) channel cause Long QT syndrome (LQT). This study reveals that the A561V mutant protein causes dominant-negative effects by promoting wild-type protein degradation, a process that can be partially reversed.
Area of Science:
- Molecular Biology
- Cardiovascular Physiology
- Genetics
Background:
- Mutations in the Human Ether-à-go-go-Related Gene (HERG) potassium channel are a primary cause of dominantly inherited Long QT syndrome (LQT), a condition associated with cardiac arrhythmias.
- Some LQT-causing mutations exhibit a dominant-negative effect, impairing the function of normal (wild-type) proteins.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying the dominant-negative behavior of the HERG A561V mutation in LQT2.
- To investigate how mutant HERG channels interfere with wild-type HERG protein expression and function.
Main Methods:
- Co-expression of wild-type HERG and the HERG A561V mutant in mammalian cells.
- Quantitative analysis of HERG K(+) current densities using electrophysiology.
- Assessment of full-length wild-type HERG protein abundance using a myc-tagged construct.
- Investigation of protein synthesis, turnover, and degradation pathways, including the role of the proteasome.
Main Results:
- HERG A561V and wild-type subunits co-assemble into functional tetramers, exhibiting near-complete dominance of the mutant.
- Co-expression of A561V significantly reduced the abundance of full-length wild-type HERG protein, correlating with current reduction.
- The reduction in wild-type protein levels resulted from both decreased synthesis and increased degradation (turnover).
- Conditions promoting protein folding (e.g., lower temperature, glycerol) and proteasome inhibition partially rescued the dominant-negative effect.
Conclusions:
- The dominant-negative effect of the HERG A561V mutation stems from the early co-assembly of mutant and wild-type subunits during protein production.
- This co-assembly leads to rapid recognition and targeting of the aberrant protein complex for degradation via the proteasome.
- Protein misfolding, cellular quality control mechanisms (proofreading), and the involvement of bystander wild-type proteins are key contributors to dominant-negative effects in LQT2.