A mutant heterodimeric myosin with one inactive head generates maximal displacement

Area of Science:

• Biochemistry
• Molecular Biology
• Cellular Mechanics

Background:

• Myosin II is a motor protein crucial for cellular movement.
• Previous studies indicated double-headed myosin generates greater displacement than single-headed myosin.
• The specific role of the second myosin head in force generation and motion remains incompletely understood.

Purpose of the Study:

• To investigate the functional contribution of the second head in double-headed myosin II.
• To determine if both heads are necessary for maximal displacement during muscle contraction.
• To elucidate the mechanism by which myosin II achieves efficient cellular motion.

Main Methods:

• Constructed a heterodimeric heavy meromyosin (HMM) with one wild-type head and one inactive (E470A mutant) head.
• Assessed in vitro motility and MgATP hydrolysis rates of the mutant and heterodimeric HMM.
• Utilized optical trap measurements to quantify unitary displacements generated by the motor proteins.

Main Results:

• Homodimeric E470A HMM exhibited minimal motility and slow MgATP hydrolysis.
• The heterodimeric HMM, with one active and one inactive head, produced unitary displacements of 10.4 nm.
• This displacement is comparable to wild-type HMM (10.2 nm) and approximately double that of single-headed subfragment-1 (4.4 nm).

Conclusions:

• A single active head in a double-headed myosin molecule is sufficient to generate near-maximal displacement.
• The second, inactive head likely optimizes the orientation and/or stabilizes the active head for efficient motion.
• These findings reveal a regulatory role for the second myosin head in maximizing motor protein efficiency.