A Tale of Two Myofilaments: Molecular Insights into Cardiac Muscle Function in Health and Disease

Abstract

Cardiac muscle function is critical for the heart to function properly but the complex mechanism behind it is still not well understood, especially at the molecular level. Additionally, it has been seen that single-point mutations disrupting the structure and function of the proteins associated with the cardiac muscles can lead to the development of cardiac diseases termed cardiomyopathies. Moreover, in recent studies, therapeutic agents targeting these proteins have also been developed to ameliorate the effect of these mutations. But to understand these mutational as well as the therapeutic effects, a detailed molecular description of the cardiac muscle function is needed. The work discussed in this dissertation focuses on the computational studies of the two protein complexes of the cardiac muscle: the thick and thin filament in the presence and absence of disease-causing mutations as well as therapeutic drugs in an effort to present a better understanding of the cardiac muscle function.The first project details the effect of cardiomyopathic mutations on the conformational change termed the recovery stroke and the ATP hydrolysis steps of the cross-bridge cycle of human cardiac β- myosin utilizing the enhanced sampling methods: metadynamics and transition path sampling. The isoformic differences in between the Dictyostelium myosin II and the human isoform were also determined, thereby providing insights into the variations in their catalytic activities. The second project utilizes similar methods as in the first project to determine the effect of a cardiac muscle activator Omecamtiv mecarbil on the alterations caused by cardiomyopathic mutations on the recovery stroke and hydrolysis steps of the cross-bridge cycle, thus, providing insights into the complex mechanism of the drug. The third project utilizes the method of transition path sampling and the developed free-energy algorithm within it to determine the effect of mavacamten on the enzymatic mechanism as well as the free-energy barriers of the same in case of the wildtype as well as cardiomyopathic mutations, thus providing a correlation between the hydrolysis mechanism and rate with the effectiveness of the drug. The fourth project is an ongoing work where a machine learning algorithm utilizing molecular dynamics simulation trajectories is being developed to aid in categorizing the pathogenicity of variants of uncertain significance as pathogenic or benign in the cardiac thin filament. The work presented here provides detailed molecular insights into the native, mutational as well as therapeutic effects on the cardiac protein complexes as well as characterizes the specific atomic-level details of the processes involved. The methodologies discussed here can also be extended to study the other transitions undergone by the sarcomeric proteins as well as various other biological processes.