Phosphorylation-dependent and ATP-induced changes in structural array in gizzard myosin filament bundles

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Myosin is a key motor protein involved in muscle contraction.
• The structure of myosin filaments is crucial for their function.
• Light chain phosphorylation is a known regulatory mechanism for myosin activity.

Purpose of the Study:

• To investigate the effect of light chain phosphorylation on the fine structure of myosin filament bundles.
• To elucidate the role of ATP in the structural organization of phosphorylated and dephosphorylated myosin.

Main Methods:

• Electron microscopy was used to observe the fine structure of myosin filament bundles.
• Experiments were conducted in the presence of 10 mM MgCl2 and ATP.

Main Results:

• Dephosphorylated myosin filament bundles exhibited a distinct striation pattern with 13.4 nm periodicity perpendicular to the filament axis when ATP was present.
• Phosphorylated myosin filament bundles did not show this regular striation pattern, even with ATP, displaying instead irregularly arranged surface projections.
• The observed 13.4 nm periodicity closely matches the dimensions of myosin heads.

Conclusions:

• The 13.4 nm striation pattern in dephosphorylated myosin likely represents a regular array of myosin heads.
• ATP induces conformational changes in dephosphorylated myosin molecules, leading to ordered head arrangement.
• Light chain phosphorylation disrupts this ATP-induced conformational change and ordered structure of myosin heads.