Rabbit skeletal muscle myosin. Unfolded carboxyl-terminus and its role in molecular assembly

Area of Science:

• Muscle Physiology
• Protein Biochemistry
• Molecular Biology

Background:

• Myosin, a key muscle protein, comprises a globular head and a rod-like tail.
• The rod portion of myosin is involved in filament formation and muscle assembly.
• Understanding the structural and functional roles of myosin domains is essential for muscle biology.

Purpose of the Study:

• To investigate the physical properties of two distinct segments of the rabbit skeletal fast muscle myosin rod portion.
• To determine the role of the C-terminus in the molecular assembly of myosin light meromyosin (LMM).
• To compare the behavior of full-length LMM (LMM-30) with a C-terminally truncated version (LMM-30C').

Main Methods:

• Expression of rabbit skeletal fast muscle myosin rod segments (LMM-30 and LMM-30C') in E. coli.
• 1H Nuclear Magnetic Resonance (NMR) spectroscopy to assess C-terminal mobility.
• Ionic strength-dependent aggregation assays at pH 8.0 to evaluate molecular assembly.

Main Results:

• 1H NMR spectroscopy revealed an unfolded and freely mobile C-terminus in LMM-30, which was absent in LMM-30C'.
• LMM-30, but not LMM-30C', formed aggregates when ionic strength was decreased at pH 8.0.
• These findings indicate that the C-terminus of LMM-30 plays a critical role in its self-assembly properties.

Conclusions:

• The C-terminus of rabbit skeletal muscle myosin rod is essential for its molecular assembly.
• The unfolded and mobile nature of the C-terminus is directly linked to the aggregation behavior of LMM-30.
• This study elucidates the structural contribution of the myosin C-terminus to filament formation.