Regulation of the actin filament pointed end dynamics in health and disease

与心脏/骨骼肌收缩有关的细纤维的改变经常产生

Alterations in the thin filaments involved in cardiac/skeletal muscle contraction often produce cardiomyopathies/nemaline myopathies with fatal consequences. Our long-term goal is to identify the components and molecular mechanisms regulating actin architecture in muscle during normal development and disease. Our short-term goal is to determine the mechanisms of how thin filament lengths are regulated by the actin filament pointed end binding proteins, leiomodin (Lmod) and tropomoduin (Tmod). Polymerization at the pointed end determines thin filament length and is regulated directly by the binding of tropomodulin (Tmod) and leiomodin (Lmod). This binding is enhanced by the integral thin filament component, tropomyosin (Tpm). We hypothesize that maintenance of thin filament length requires the antagonistic action of Tmod and Lmod; that is, the role of Tmod is to prevent elongation at the pointed end while Lmod allows elongation. We also predict that Tmod and Lmod binding and action at the pointed end is determined by different arrangements of their Tpm- and actin-binding sites. To achieve our goals, a powerful, multidisciplinary collaboration has been established between the Kostyukova laboratory at Washington State University (with expertise in protein structure, structural biochemistry and biophysical properties of actin filaments and regulatory proteins) and the Gregorio laboratory at the University of Arizona (with expertise in the molecular, cellular and developmental biology of myofibril assembly). In this proposal we will combine a broad range of state-of-the-art approaches such as determination of high-resolution atomic structure of Lmod /Tpm binding interface, and use of advanced microscopy and physiological assessment of myocytes from Lmod2 or Lmod3 null mice to test our molecular designs. The proposed experiments will connect Lmod-related thin filament alterations with familial myopathies. A better understanding of thin filament function and of its regulation is critical to better understand muscle disease pathogenesis, to improve diagnostics and to potentially identify novel drug targets.