Sequence requirements for the thick filament assembly of sarcomeric myosin

Abstract

In order to define the sequence requirements of sarcomeric myosin thick filament assembly, a number of segments of a human adult fast skeletal myosin rod were expressed in Escherichia coli. The isolated proteins were analyzed for their solubility at varying salt, Mg{dollar}\sp{lcub}+2{rcub}{dollar}, and pH conditions; and for their ability to form periodic structures with repeats characteristic of LMM (43 nm and 14 nm). Of the 1937 amino acids of the full length MHC, residues 1589-1902 were necessary and sufficient for both the solubility and periodic properties of the myosin rod. Residues 1709-1902 form paracrystals with the 14 nm, but not the 43 nm, periodicity of myosin and possess altered solubility properties relative to myosin. These residues (1709-1902) thus separate the solubility and periodic properties of LMM. To define further both the size and sequence requirements for assembly, amino- and carboxy-terminal deletions of the 313 amino acid assembly-competent construct were made. Analysis suggests that both a specific sequence (29 residues, 1873-1902) and a minimum size of myosin rod are required for assembly into paracrystals. These 29 residues can confer the ability to assemble into paracrystals to a hybrid construct in which these 29 residues were added to an assembly-incompetent fragment. The ability of two overlapping myosin rod segments to interact was also assessed. When mixed together in various ratios, it was found that an assembly-competent fragment was unable to restore the assembly properties of the assembly-incompetent segment. These bacterially-expressed rod fragments were also useful in the characterization of monoclonal antibodies MF20 (Bader et al., 1982) and F27 (Miller et al., 1989) to residues 1274-1471 and 1839-1902, respectively.