Precise Binding of Tropomyosin on Actin Involves Sequence-Dependent Variance in Coiled-Coil Twisting

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Dynamics

Background:

• Tropomyosin is a coiled-coil protein crucial for muscle regulation.
• It exhibits noncanonical residues, like D137, at its helical interface.
• The role of D137 in tropomyosin's function and stability remains unclear.

Purpose of the Study:

• To investigate the dynamic behavior of tropomyosin, particularly the D137 residue.
• To understand the impact of D137 on tropomyosin's interaction with actin filaments.
• To elucidate the role of D137 in the regulation of muscle contraction.

Main Methods:

• Molecular dynamics simulations of actin-free and actin-associated tropomyosin.
• Analysis of tropomyosin's coiled-coil twist and flexibility.
• Assessment of actin-tropomyosin electrostatic interactions.

Main Results:

• The noncanonical D137 residue influences tropomyosin's twist variation.
• D137-induced twisting optimizes electrostatic contacts with actin.
• D137 increases tropomyosin stiffness on actin filaments, enhancing regulation.

Conclusions:

• D137-sponsored twisting enhances tropomyosin's regulatory function on actin.
• This twisting optimizes protein-protein interactions within the thin filament.
• Tropomyosin's coiled-coil structure is dynamically regulated by specific residues like D137.