Segmental flexibility and head-head interaction in scallop myosin. A study using saturation transfer electron...

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Myosin head domain rotational motion is crucial for muscle contraction.
• Scallop myosin's ATPase activity is regulated by light chains and calcium sensitivity.
• Previous studies indicated independent motion of myosin head domains in rabbit muscle.

Purpose of the Study:

• To investigate the rotational motion of scallop myosin head domains in native and desensitized states.
• To understand the role of regulatory light chains in myosin's molecular dynamics.
• To explore potential mechanisms for altered rotational motion upon desensitization.

Main Methods:

• Saturation transfer electron paramagnetic resonance (EPR) spectroscopy was employed.
• Scallop myosin was spin-labelled with a specific nitroxide probe.
• Analytical ultracentrifugation was used to assess myosin aggregation state.

Main Results:

• Native scallop myosin head domains exhibited independent rotational motion.
• Desensitization by removing a regulatory light chain significantly increased rotational correlation time (pi) of myosin.
• Recombination of the light chain restored Ca2+ sensitivity and initial correlation time; desensitized heavy meromyosin showed increased pi and partial ATPase desensitization.

Conclusions:

• Removal of a regulatory light chain induces an intramolecular conformational change, restricting myosin head domain motion.
• This restriction may involve a conformational change in the subfragment 1-subfragment 2 hinge region or head-head association.
• The findings suggest a link between regulatory light chain binding, myosin conformation, and ATPase activity regulation.