Phosphorylated smooth muscle myosin can exist in a stable folded 10 S conformation at low salt concentrations (<0.1 M KCl), and unfolds to an extended 6 S form above 0.3 M KCl.
The study demonstrates that the conformational state of smooth muscle myosin depends on both phosphorylation and ionic strength, with phosphorylated myosin able to maintain a folded 10 S conformation at low salt concentrations.
Stoichiometric amounts of MgATP disassemble dephosphorylated smooth muscle and nonmuscle myosin filaments to a 10 S monomer. Phosphorylation of the regulatory light chain reassembles the myosin into filaments (Suzuki, H., Onishi, H., Takahashi, K., and Watanabe, S. (1978) J. Biochem. (Tokyo) 84, 1529-1542). The conformation of the dephosphorylated 10 S monomer is highly unusual in that the 1500 A long myosin tail is folded into approximately equal thirds (Onishi, H., and Wakabayashi, T. (1982) J. Biochem. (Tokyo) 92, 871-879; Trybus, K. M., Huiatt, T. W., and Lowey, S. (1982) Proc. Natl. Acad. Sci. U. S. A. 79, 6151-6155). It was recently reported that phosphorylation of the regulatory light chain causes the bent monomer to unfold to the extended conformation characteristic of 6 S myosin in high salt (Craig, R., Smith, R., and Kendrick-Jones, J. (1983) Nature (Lond.) 302, 436-439). Here we show that phosphorylated myosin can exist in a stable 10 S conformation provided that the salt concentration is kept sufficiently low. Only in a narrow range of salt concentration does the monomer conformation depend on the state of phosphorylation. Above 0.3 M KCl, all myosins revert to the extended form; below 0.1 M KCl, all monomeric myosin is folded. As the salt concentration is decreased to 0.05 M KCl, the 10 S monomers form antiparallel folded dimers. Because phosphorylation increases filament formation even when 10 S monomer remains in equilibrium with polymer, assembly could proceed via the association of 10 S monomers or by a transient 6 S intermediate.
Trybus et al. (Sun,) reported a other. Phosphorylation and ionic strength (KCl concentration) was evaluated on Myosin conformation (10 S vs 6 S). Phosphorylated smooth muscle myosin can exist in a stable folded 10 S conformation at low salt concentrations (<0.1 M KCl), and unfolds to an extended 6 S form above 0.3 M KCl.