REGULATION OF THE ACTIN FILAMENT POINTED END DYNAMICS IN HEALTH AND DISEASE

点击翻译按钮获取中文摘要

In striated muscles, actin thin filament architecture is critical for efficient contractile activity, and alterations in thin filament integrity are linked to severe and often lethal skeletal and cardiac muscle diseases. Our long-term goal is to identify the components and molecular mechanisms regulating actin architecture in striated muscle during normal development and disease. Our short-term goal is to evaluate how actin-binding proteins of the tropomodulin family (e.g. leiomodin or Lmod and tropomoduin or Tmod) affect the formation and then the structure of the thin filament. We will test our recently proposed molecular mechanism for the Lmod/Tmod-dependent regulation of the pointed end of the thin filaments. We will also study the structural and functional consequences of Lmod binding to sides of the already formed thin filaments. Finally, we will establish mechanisms of regulation of Lmod functions. We propose three aims to identify underlying molecular mechanisms of the full spectrum of Lmod and Tmod functions: (1) to decipher the role of Lmod in the maintenance of proper thin filament lengths via pointed end regulation; (2) to establish the role of Lmod’s actin-binding sites in thin filament activation; (3) to test the hypothesis that Lmod functions are regulated by Ca2+. By employing high resolution cryogenic electron microscopy (cryo-EM) in conjunction with 3-dimensional nuclear magnetic resonance and Förster resonance energy transfer), we will recreate the full picture of Ca2+- dependent Lmod interactions with the thin filament and reveal the biological significance of these interactions. The robustness of structural models will be evaluated by monitoring of development and contractility of cardiac and skeletal muscles in knockout mice in vivo via the identification and utilization of mutations specifically affecting newly discovered Lmod’s and Tmod’s functionalities. To achieve these goals, we established a powerful multidisciplinary collaboration between the Kostyukova laboratory at the Washington State University (expert in protein structure, biochemical and biophysical properties of actin-binding proteins), the Gregorio laboratory at the University of Arizona (expert in the molecular, cellular and developmental biology of myofibril assembly) and the Galkin laboratory at the Eastern Virginia Medical School (expert in high resolution cryo-EM of actin complexes). Our data will provide a comprehensive identification of critical components of the regulatory mechanisms underlying thin filament assembly and maintenance in health and disease.