Nucleotide- and temperature-induced changes in myosin subfragment-1 structure

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Myosin subfragment 1 (S1) is crucial for muscle contraction, undergoing conformational changes upon nucleotide binding.
• Understanding the dynamics of S1 is key to elucidating the mechanisms of force generation in muscle.
• Intrinsic tryptophan residues in S1 serve as probes for monitoring structural dynamics.

Purpose of the Study:

• To investigate the effects of nucleotide binding (MgADP, MgADP,P, MgADP,V) and temperature on the internal structural dynamics of myosin subfragment 1 (S1).
• To characterize global conformational changes using transient electric birefringence.
• To identify structural features of S1-MgADP,P relevant to actin binding and force generation.

Main Methods:

• Intrinsic tryptophan phosphorescence lifetime and fluorescence anisotropy measurements to assess internal dynamics.
• Transient electric birefringence to determine the rate of rotational diffusion and monitor global conformation.
• Measurements conducted across a temperature range (0-25°C) with various nucleotide ligands.

Main Results:

• Nucleotide binding (MgADP, MgADP,P, MgADP,V) progressively rigidifies S1 structure.
• Increasing temperature enhances internal mobility of S1 tryptophans.
• A reversible temperature-dependent transition near 15°C was observed, indicating local, not global, conformational changes in S1, S1-MgADP, and S1-MgADP,P, but not S1-MgADP,V.

Conclusions:

• Nucleotide binding induces significant structural stabilization in S1.
• The observed 15°C transition represents localized conformational rearrangements within S1.
• These findings provide insights into the structural basis of S1's function in the actin-myosin interaction and force production.