Large-scale purification of functional human P-glycoprotein (ABCB1)

Area of Science:

• Membrane protein biochemistry
• Drug transport mechanisms
• Structural biology

Background:

• Human P-glycoprotein (P-gp) is an ATP-binding cassette transporter involved in multidrug resistance and drug pharmacokinetics.
• Understanding P-gp's drug efflux mechanism is hindered by challenges in large-scale purification and maintaining protein activity.
• Previous purification methods often result in protein inactivation and aggregation, limiting functional and structural studies.

Purpose of the Study:

• To establish a convenient and robust method for large-scale purification of functionally active human P-gp.
• To obtain homogeneous wild-type P-gp and a mutant defective in ATP hydrolysis (E556Q/E1201Q) for detailed characterization.
• To provide purified P-gp suitable for biochemical, biophysical, and structural analyses.

Main Methods:

• Large-scale expression of human P-gp in High-Five insect cells using recombinant baculovirus.
• Solubilization and purification using three detergents: 1,2-diheptanoyol-sn-glycero-3-phosphocholine, dodecyl maltoside, and n-octyl-β-d-glucopyranoside.
• Purification strategy involving immobilized metal affinity chromatography followed by anion exchange or size exclusion chromatography.

Main Results:

• Homogeneous, functionally active wild-type P-gp and its ATP hydrolysis-defective mutant were obtained in high concentrations (2-12 mg/mL).
• Size exclusion chromatography proved superior for separating monomeric P-gp from aggregates.
• Reconstituted P-gp in proteoliposomes and nanodiscs demonstrated basal and substrate/inhibitor-modulated ATPase activity.

Conclusions:

• A scalable and reliable purification protocol for human P-gp has been developed.
• The purified, active P-gp is suitable for comprehensive biochemical, biophysical, and structural investigations.
• This method facilitates deeper understanding of P-gp's role in drug transport and resistance.