3-Dimensional Structure of Human Cardiac Muscle Myosin Filaments by Electron Microscopy and Single Particle Analysis

Abstract

In all muscles the interaction between actin and myosin filaments leads to muscle contraction and force production mediated by the hydrolysis of ATP. Actin filament structure is well understood to high resolution, but myosin filament structure is much less well defined. Myosin filaments are formed from complicated arrangements of myosin molecules and accessory proteins (e.g. C-protein [MyBP-C] and titin). We compare the arrangement of the myosin heads in the different species and how these arrangements change in diseased muscle. We have developed a method to solve the 3-dimensional (3D) structure of myosin filaments by single particle analysis of electron microscope (EM) data. We already defined the 3D structure of myosin filaments of various muscles from different species by both X-ray diffraction modelling and EM and single particle analysis including insect flight muscle, scallop striated muscle, fish skeletal muscle and rabbit cardiac muscle. We are now studying the 3D structure of myosin filaments isolated from human heart muscles.Mutations in cardiac myosin, C-protein and titin are known to be associated with cardiomyopathies (e.g. hypertrophic cardiomyopathy and dilated cardiomyopathy). In order to understand myosin-associated heart disease, it is important to understand the 3D structure of myosin filaments in normal heart muscle.Recently we have developed procedures to isolate human cardiac muscle myosin filaments preserving their highly ordered pseudo-helical structure thus making them amenable, for the first time, to EM and single particle image analysis. We have collected EM data from myosin filaments isolated from both normal and failing hearts, and have so far processed the data from normal heart muscle. Analysis of the 3D structure of myosin filaments in normal heart muscle will permit the structural effects of known myosin filaments-associated mutations to be investigated in detail.