Myosin: Structure, Function, Regulation and Disease

Abstract

The human myosin superfamily is made up of 12 different classes of myosin. Class 2 is the largest, and is made up of 13 genes. Of these, 9 are expressed in striated muscle and the remaining 4 in non‐muscle cells and smooth muscle. All of these myosins form filaments. In striated muscle, the filaments contain precisely 294 molecules. In contrast, non‐muscle myosins form much shorter filaments (about 30 molecules). The activity of all of these myosins is regulated by an interaction of the heads (comprising the motor domain and lever) with the first part of the coiled coil (subfragment 2, S2) to form the so‐called ‘interacting heads’ motif. Non‐muscle and smooth muscle myosin heads are additionally regulated by an interaction of the head with the tail forming region (light meromyosin, LMM).We use a combination of cell biology, and structural approaches, including electron microscopy to understand the effects of disease‐causing mutations in S2 and in LMM. Mutations in striated myosins (MyHCβ, MyHC2a) cause cardiac and skeletal muscle diseases respectively, although mutations in the distal LMM region of MyHCβ are predominantly associated with skeletal muscle disease. Mutations in non‐muscle myosin (NM2A) cause a range of bleeding disorders. We determine how specific mutations affect the myosin’s ability to form filaments, and how they affect formation of the regulated state of the myosin. For example, we use circular dichroism to determine if specific mutations affect the secondary structure of LMM. We use negative stain electron microscopy to evaluate filament formation by the LMM (fused to GST, to prevent paracrystal formation), and we use GFP‐tagged MHC to evaluate the ability of each mutant to incorporate into filaments in cultured cells, myotubes and adult rat cardiomyocytes (Parker et al. (2018) J. Mol. Biol). Together with additional structural studies, we are starting to understand how specific mutations affect myosin function, to gain a better understanding of the disease process.Support or Funding InformationThis research is supported by the Medical Research Council, MR/R009406/1 and MR/S023593/1 to MP.