Abstract
X-ray diffraction and tension measurement experiments were conducted on rat left ventricular skinned fibers with or without “troponin-T treatment,” which exchanges the endogenous troponin T/I/C complex with exogenous troponin-T. These experiments were performed to observe the structural changes in troponin-T within a fiber elicited by contractile crossbridge formation and investigate the abnormality of hypertrophic cardiomyopathy-related troponin-T mutants. The intensity of the troponin reflection at 1/38.5 nm−1 was decreased significantly by ATP addition after treatment with wild-type or mutant troponin-T, indicating that crossbridge formation affected the conformation of troponin-T. In experiments on cardiac fibers treated with the hypertrophic cardiomyopathy-related mutants E244D- and K247R-troponin-T, treatment with K247R-troponin-T did not recruit contracting actomyosin to a greater extent than wild-type-troponin-T, although a similar drop in the intensity of the troponin reflection occurred. Therefore, the conformational change in K247R-troponin-T was suggested to be unable to fully recruit actomyosin interaction, which may be the cause of cardiomyopathy.
Highlights
The regulatory mechanism underlying contraction by troponin-tropomyosin in striated muscle has not been completely elucidated yet
As for troponin, which is involved in the pathogenesis of familial cardiomyopathy, pieces of structural evidence that suggest formation of contractile crossbridges is involved in the regulatory mechanism of contraction have been accumulated to date [1,2,3,4,5,6]
In cardiac muscle, the change in intensity of the troponin reflection accompanied by crossbridge formation has not been clearly elucidated because obtaining a detailed X-ray diffraction pattern is far more difficult compared to skeletal muscle, due to the lower density of cardiac myofibrils and their susceptibility to a lack of oxygen
Summary
The regulatory mechanism underlying contraction by troponin-tropomyosin in striated muscle has not been completely elucidated yet. As for troponin, which is involved in the pathogenesis of familial cardiomyopathy, pieces of structural evidence that suggest formation of contractile crossbridges is involved in the regulatory mechanism of contraction have been accumulated to date [1,2,3,4,5,6]. Previous X-ray diffraction analyses on vertebrate skeletal muscle reported that the intensity of the meridional reflection of troponin at. In cardiac muscle, the change in intensity of the troponin reflection accompanied by crossbridge formation has not been clearly elucidated because obtaining a detailed X-ray diffraction pattern is far more difficult compared to skeletal muscle, due to the lower density of cardiac myofibrils and their susceptibility to a lack of oxygen
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