Cardiomyopathy-causing mutations in the beta-cardiac myosin tail that reduce helical content in vitro reduce sarcomere incorporation of myosin in vivo.
Mutations in the coiled-coil tail of beta-cardiac myosin that reduce helical content impair sarcomere incorporation, providing a potential mechanism for how these mutations lead to cardiomyopathy.
It is unclear why mutations in the filament-forming tail of myosin heavy chain (MHC) cause hypertrophic or dilated cardiomyopathy as these mutations should not directly affect contraction. To investigate this, we first investigated the impact of five hypertrophic cardiomyopathy-causing (N1327K, E1356K, R1382W, E1555K, and R1768K) and one dilated cardiomyopathy-causing (R1500W) tail mutations on their ability to incorporate into muscle sarcomeres in vivo . We used adenoviral delivery to express full-length wild type or mutant enhanced GFP-MHC in isolated adult cardiomyocytes. Three mutations (N1327K, E1356K, and E1555K) reduced enhanced GFP-MHC incorporation into muscle sarcomeres, whereas the remainder had no effect. No mutations significantly affected contraction. Fluorescence recovery after photobleaching showed that fluorescence recovery for the mutation that incorporated least well (N1327K) was significantly faster than that of WT with half-times of 25.1 ± 1.8 and 32.2 ± 2.5 min (mean ± S.E.), respectively. Next, we determined the effects of each mutation on the helical properties of wild type and seven mutant peptides (7, 11, or 15 heptads long) from the myosin tail by circular dichroism. R1382W and E1768K slightly increased the α-helical nature of peptides. The remaining mutations reduced α-helical content, with N1327K showing the greatest reduction. Only peptides containing residues 1301–1329 were highly α-helical suggesting that this region helps in initiation of coiled coil. These results suggest that small effects of mutations on helicity translate into a reduced ability to incorporate into sarcomeres, which may elicit compensatory hypertrophy. Background: It is unclear how mutations in the coiled-coil tail of β-cardiac myosin cause heart disease. Results: Effects of disease-causing mutations in the myosin tail were studied in vivo and in vitro . Conclusion: Mutations that reduce helical content in vitro reduce sarcomere incorporation of myosin in vivo . Significance: A change in myosin tail structure can lead to heart disease.
Wolny et al. (Thu,) conducted a other in Hypertrophic and dilated cardiomyopathy. Myosin heavy chain tail mutations vs. Wild type myosin heavy chain was evaluated on Incorporation into muscle sarcomeres and helical properties. Cardiomyopathy-causing mutations in the beta-cardiac myosin tail that reduce helical content in vitro reduce sarcomere incorporation of myosin in vivo.
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