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Heterologous expression of a cardiomyopathic myosin that is defective in its actin interaction
H L Sweeney1, A J Straceski, L A Leinwand
1Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia 19104-6085.
Insights
A specific cardiac myosin mutation (Arg-403 to Gln) impairs muscle function by reducing actin interaction, leading to decreased power output and potentially causing hypertrophic cardiomyopathy.
Area of Science:
- Biochemistry
- Molecular Biology
- Cardiology
Background:
- A point mutation in cardiac myosin (Arg-403 to Gln) is associated with human hypertrophic cardiomyopathy.
- Understanding the functional consequences of this mutation is crucial for elucidating disease mechanisms.
Purpose of the Study:
- To investigate the functional impact of the Arg-403 to Gln mutation on cardiac myosin function.
- To characterize the effects of this mutation on ATPase activity and in vitro motility.
Main Methods:
- Utilized baculovirus-driven coexpression of myosin heavy and light chains.
- Assessed cardiac myosin ATPase activity in the presence and absence of actin.
- Measured in vitro motility of cardiac myosin.
Main Results:
- The Arg-403 to Gln mutation did not affect basal ATPase activity without actin.
- Actin-activated ATPase activity was significantly reduced (Vmax decreased >3.5-fold, K(app) increased >3-fold).
- In vitro motility was reduced nearly 5-fold.
Conclusions:
- The Arg-403 residue is critical for myosin's interaction with actin.
- The mutation likely alters the kinetics of the actin-myosin crossbridge cycle.
- This mutation may lead to decreased cardiac muscle power output, contributing to hypertrophy.
Abstract:
A point mutation in the heavy chain of cardiac myosin, resulting in replacement of an arginine (Arg) with glutamine (Gln), has been linked to hypertrophic cardiomyopathy in humans (Geisterfer-Lowrance, A. A. T., Kass, S., Tanigawa, G., Vosberg, H.-P., McKenna, W., Seidman, J. G., and Seidman, C. E. (1990) Cell 62, 999-1006). To determine the functional impact of this mutation, baculovirus-driven coexpression of myosin heavy and light chains has been developed. The Arg-403-->Gln mutation resulted in cardiac myosin with normal ATPase activity in the absence of actin. However, in the presence of actin, ATPase activity was greatly reduced (Vmax decreased > 3.5-fold and K(app) increased > 3-fold). In vitro motility was reduced nearly 5-fold by this single amino acid mutation. Thus, Arg-403 likely contributes to an important interaction at the actin interface of myosin. Replacement of Arg-403 with Gln leads to decreased rate(s) of transition within the actin-myosin crossbridge cycle. In humans, this mutation will result in decreased power output per unit area of cardiac muscle, likely providing a stimulus for hypertrophy.