Insights into Various Types of Myopathy using the Atomic Model of Lethocerus Myosin Filaments

Abstract

There are more than 500 disease-causing mutations in human striated muscle myosin II genes and approximately 200 of them are in the tail region. Myosin tails comprise most of the thick filament backbone which (compared to the rest of the filament) is poorly understood. We have resolved myosin filaments isolated from Lethocerus flight muscle to near-atomic resolution and built an atomic model that shows the predicted coiled-coil geometry, as well as interactions between myosin tails in the backbone. Contacts between myosin tails involve predominately salt bridges. Amino-acid sequence similarity between Lethocerus flight muscle myosin II and human β-myosin is 75%, but for charged amino-acids, this value is above 90%. This shows the functional importance of the charged amino-acids so the stability and function of the myosin filament. The cryoEM structure of myosin filaments provides a unique opportunity to study these myopathy causing mutations in their native context. These mutations cause various diseases like hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), skeletal myopathy (SM), and myosin storage myopathy (MSM). We observed a correlation between the frequency of salt bridges and identified mutations in the tail region. Resolving the C-terminal area on the myosin known as Assembly Competence Domain (ACD) reveals novel information about MSM, which targets the backbone exclusively. Out of six known mutations that cause MSM, three are observed to be involved in inter-tail salt bridges, and two seem to alter the coiled-coil packing. The latter happens either through deletion or substitution with Proline and can disrupt the salt bridges in the ACD region. The atomic model built in the Lethocerus myosin filament can be used as a model to understand diseases like MSM. Supported by NIH.