P-glycoprotein-ATPase modulation: the molecular mechanisms

Area of Science:

• Biochemistry
• Membrane Transport
• Biophysics

Background:

• P-glycoprotein-ATPase is a broad-specificity efflux transporter crucial for cellular defense.
• Understanding allocrit transport rates is vital, as they generally decrease with increasing transporter affinity.
• Detergents are commonly used to study membrane proteins but can affect their activity.

Purpose of the Study:

• To investigate the mechanism behind the unexpected down-modulation of P-glycoprotein-ATPase activity by certain detergents.
• To determine the relationship between detergent properties and their effect on transporter function.
• To elucidate the role of detergent partitioning and binding energetics in modulating P-glycoprotein-ATPase activity.

Main Methods:

• Studied 34 neutral and cationic detergents with varying hydrophobic/hydrophilic characteristics.
• Measured P-glycoprotein-ATPase activity as a function of detergent concentration.
• Assessed the free energy of detergent partitioning into the lipid membrane and binding to the transporter.
• Utilized (2)H-NMR-spectroscopy to exclude membrane disordering as a cause of inhibition.

Main Results:

• Seven detergents activated the ATPase, while 27 closely related detergents significantly reduced its activity.
• The ratio (q) of free energies of detergent binding to the membrane and transporter determined ATP hydrolysis rates.
• Neutral detergents with q = 2.7 ± 0.2 (q > 3) followed exponential dependence; deviations altered activity.
• Membrane disordering by detergents was ruled out as the cause of P-glycoprotein-ATPase inhibition.

Conclusions:

• The ratio of free energy of binding dictates P-glycoprotein-ATPase modulation by detergents.
• Specific detergent properties are critical for transporter activation or inhibition.
• These findings offer insights into transporter modulation by both detergents and drugs.