Fast vesicle transport in PC12 neurites: velocities and forces

Area of Science:

• Cell Biology
• Biophysics
• Neuroscience

Background:

• Understanding motor protein mechanics within living cells is crucial but challenging.
• Previous studies focused on isolated motor proteins in vitro, limiting insights into in vivo behavior.
• Intracellular transport relies on motor proteins like kinesin moving cargo along microtubules.

Purpose of the Study:

• To investigate the mechanical behavior of single motor-driven vesicles in live PC12 cell neurites.
• To determine the forces and velocities associated with intracellular vesicle transport.
• To estimate the efficiency of motor proteins during cargo transport in a cellular environment.

Main Methods:

• High-resolution tracking of single vesicles in PC12 neurites (±30 nm spatial, 120 ms temporal precision).
• Measurement of vesicle velocities over extended periods (up to 15 s) and distances (up to 15 µm).
• Analysis of Brownian motion to determine the viscoelastic modulus and drag forces using Stokes-Einstein-Sutherland relations.

Main Results:

• Vesicle velocities exhibited step-like changes, suggesting alterations in the number of active motor proteins.
• The drag force at the lowest sustained velocity was measured to be 4.2±0.6 pN for vesicles (0.30-0.40 µm radius).
• Estimated motor protein efficiency for kinesin in PC12 neurites is approximately 35%.

Conclusions:

• Observed velocity steps likely correspond to changes in the number of active kinesin motors (±1 or ±2).
• Motor protein efficiency in vivo is significantly lower than in vitro, highlighting cellular constraints.
• This study provides quantitative mechanical data for motor-driven transport within a neuronal context.