The "electrostatic-switch" mechanism: Monte Carlo study of MARCKS-membrane interaction

Area of Science:

• Biophysics
• Computational Biology
• Cell Biology

Background:

• The myristoylated alanine-rich C kinase substrate (MARCKS) is a key regulator of membrane-associated cellular processes.
• Understanding MARCKS' interaction with phospholipid membranes is crucial for deciphering its biological functions.

Purpose of the Study:

• To model the binding of MARCKS to mixed, fluid phospholipid membranes using a Monte Carlo simulation scheme.
• To elucidate the physical mechanisms governing MARCKS-membrane interactions and the role of phosphorylation.

Main Methods:

• A Monte Carlo simulation scheme was employed to model MARCKS as a flexible chain of beads.
• MARCKS-membrane interactions were simulated using Debye-Hückel electrostatic potentials and semiempirical hydrophobic energies.
• Simulations included neutral, monovalent, and tetravalent lipids, all laterally mobile.

Main Results:

• MARCKS membrane binding is driven by electrostatic attraction to acidic lipids and hydrophobic penetration.
• Binding is opposed by entropic losses, electrostatic repulsion from lipid chains, and lipid demixing.
• Phosphorylation of MARCKS triggers an "electrostatic switch", weakening membrane interaction and PIP(2) sequestration.

Conclusions:

• The simulation provides a physical model for MARCKS-membrane complex formation.
• This model captures the "discreteness of charge" at membrane surfaces.
• The findings offer insights into membrane-mediated macromolecular complex formation in cellular processes.