Probing cholesterol binding and translocation in P-glycoprotein

Area of Science:

• Biophysics
• Molecular Biology
• Membrane Protein Dynamics

Background:

• P-glycoprotein (Pgp), an ABC transporter, is crucial in cancer multidrug resistance.
• Cholesterol modulates Pgp activity, but its binding sites and transport mechanisms are poorly understood.

Purpose of the Study:

• To investigate cholesterol-protein interactions and redistribution mechanisms at Pgp using extensive molecular dynamics simulations.
• To identify specific cholesterol binding regions and characterize cholesterol translocation events mediated by Pgp.

Main Methods:

• Conducted 40 independent molecular dynamics (MD) simulations of Pgp in cholesterol-rich lipid bilayers, totaling 8 μs.
• Utilized clustering analysis to identify cholesterol-binding sites and observed cholesterol flipping events.

Main Results:

• Identified specific, asymmetric cholesterol-binding regions involving transmembrane helices TM1-6 and TM8.
• Observed cholesterol binding primarily via its rough β-face and captured full/partial cholesterol flipping events mediated by Pgp surface helices TM1, TM2, and TM11.
• Found that sequence-based motifs (CRAC/CARC) do not fully predict all observed binding sites.

Conclusions:

• Provides the first direct observation of unconventional cholesterol translocation on Pgp, proposing a secondary transport model for ABC exporters.
• Highlights the limitations of current motifs for predicting cholesterol binding sites and emphasizes the role of Pgp in cholesterol redistribution.