PDK1:PKCα heterodimer association-dissociation dynamics in single-molecule diffusion tracks on a target membrane

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Biophysics

Background:

• Protein kinases PDK1 and PKCα form heterodimers on lipid bilayers.
• PDK1's PH domain binds PIP3 lipids with low membrane drag.
• PKCα's C1 and C2 domains insert into the bilayer, causing high drag.

Purpose of the Study:

• Investigate the association-dissociation kinetics of the PDK1:PKCα heterodimer.
• Determine the rate constants for heterodimer formation and dissociation.
• Understand the role of diffusion changes in membrane signaling.

Main Methods:

• Monitoring two-dimensional diffusion of single, membrane-associated fluorescently labeled PDK1 molecules.
• Analyzing diffusivity changes upon PKCα binding and unbinding.
• Applying two-state hidden Markov modeling and dwell time analysis to diffusion trajectories.

Main Results:

• Individual PDK1 molecules switch between high (monomer) and low (heterodimer) diffusivity states.
• Both monomer and heterodimer states decay via simple exponential kinetics.
• Rate constants for association and dissociation were estimated.

Conclusions:

• The study elucidates the association-dissociation kinetics of the PDK1:PKCα heterodimer.
• This has significant implications for understanding the PDK1/AKT1/mTOR pathway and cancer.
• Single-molecule diffusion measurements are powerful for studying membrane signaling kinetics.