Random walk of processive, quantum dot-labeled myosin Va molecules within the actin cortex of COS-7 cells

Area of Science:

• Cell Biology
• Molecular Motors
• Biophysics

Background:

• Myosin Va (myoVa) is a key actin-based motor protein responsible for intracellular transport.
• While in vitro studies detail myoVa's processive movement, its behavior within the complex cellular environment remains less understood.

Purpose of the Study:

• To investigate the in vivo dynamics of single Myosin Va motors within living cells.
• To characterize the movement patterns and step characteristics of Myosin Va in a cellular context.

Main Methods:

• Utilized quantum dot (Qdot)-labeled Myosin Va HMM (heavy meromyosin) for direct tracking.
• Employed total internal reflectance fluorescence microscopy (TIRFm) with high spatial and temporal resolution.
• Performed single-particle tracking and Monte Carlo modeling.

Main Results:

• Observed short (
• Measured a mean velocity of 604 nm/s, independent of the number of myoVa molecules per Qdot.
• Documented sequential 75 nm steps per head at a rate of 16 s(-1), mirroring in vitro observations.
• Monte Carlo modeling suggested random walk behavior in the cortical actin network.

Conclusions:

• Single Myosin Va motors exhibit processive, stepping motion within living cells.
• The observed intracellular movement is consistent with a random walk through the cortical actin cytoskeleton.
• This study provides crucial insights into the intracellular operation of Myosin Va.