The flexibility of two tropomyosin mutants, D175N and E180G, that cause hypertrophic cardiomyopathy
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118 (United States)
- School of Biosciences, University of Kent, Canterbury, Kent CT2 7NJ (United Kingdom)
- National Heart and Lung Institute, Imperial College London, London W12 0NN (United Kingdom)
- Computational Biochemistry Group, University of Heidelberg, Heidelberg D-69120 (Germany)
Highlights: Black-Right-Pointing-Pointer Well-known tropomyosin mutants, D175N and E180G are linked to cardiomyopathies. Black-Right-Pointing-Pointer The structural mechanics of D175N and E180G tropomyosins have been investigated. Black-Right-Pointing-Pointer D175N and E180G mutations increase both local and global tropomyosin flexibility. Black-Right-Pointing-Pointer In muscle, this increased flexibility will enhance myosin interactions on actin. Black-Right-Pointing-Pointer Extra myosin interaction can alter cardiac Ca{sup 2+}-switching, leading to dysfunction. -- Abstract: Point mutations targeting muscle thin filament proteins are the cause of a number of cardiomyopathies. In many cases, biological effects of the mutations are well-documented, whereas their structural and mechanical impact on filament assembly and regulatory function is lacking. In order to elucidate molecular defects leading to cardiac dysfunction, we have examined the structural mechanics of two tropomyosin mutants, E180G and D175N, which are associated with hypertrophic cardiomyopathy (HCM). Tropomyosin is an {alpha}-helical coiled-coil dimer which polymerizes end-to-end to create an elongated superhelix that wraps around F-actin filaments of muscle and non-muscle cells, thus modulating the binding of other actin-binding proteins. Here, we study how flexibility changes in the E180G and D175N mutants might affect tropomyosin binding and regulatory motion on F-actin. Electron microscopy and Molecular Dynamics simulations show that E180G and D175N mutations cause an increase in bending flexibility of tropomyosin both locally and globally. This excess flexibility is likely to increase accessibility of the myosin-binding sites on F-actin, thus destabilizing the low-Ca{sup 2+} relaxed-state of cardiac muscle. The resulting imbalance in the on-off switching mechanism of the mutants will shift the regulatory equilibrium towards Ca{sup 2+}-activation of cardiac muscle, as is observed in affected muscle, accompanied by enhanced systolic activity, diastolic dysfunction, and cardiac compensations associated with HCM and heart failure.
- OSTI ID:
- 22210171
- Journal Information:
- Biochemical and Biophysical Research Communications, Vol. 424, Issue 3; Other Information: Copyright (c) 2012 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0006-291X
- Country of Publication:
- United States
- Language:
- English
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