Domain exchangeability between the multidrug transporter (MDR1) and phosphatidylcholine flippase (MDR2)

Area of Science:

• Biochemistry
• Molecular Biology
• Cancer Research

Background:

• Multidrug resistance (MDR) mediated by P-glycoprotein (MDR1) poses a significant challenge in cancer treatment.
• MDR1 homolog MDR2 (MDR3) functions as a phosphatidylcholine flippase, offering insights into MDR1 substrate specificity.
• Previous studies identified key residues in MDR1's transmembrane domain 6 (TM6) essential for multidrug transport.

Purpose of the Study:

• To further elucidate the exchangeability between MDR1 and MDR2 by constructing and analyzing MDR1/MDR2 chimeras.
• To determine the structural basis for MDR1's substrate specificity and transport activity.

Main Methods:

• Construction and analysis of MDR1/MDR2 chimeras.
• Site-directed mutagenesis to investigate specific residue functions.
• Assessment of drug binding affinity, ATPase activity, and transport function.

Main Results:

• The N-terminal halves of MDR1 and MDR2 are largely exchangeable, with notable exceptions in TM6.
• The C-terminal halves of MDR1 and MDR2 show limited exchangeability.
• MDR2 with substituted MDR1 residues (318-332 in TM6 and 937-994 in TM11-12) exhibited substrate binding but lacked transport activity.

Conclusions:

• Specific residues in MDR1's TM6 are critical for its multidrug transport function.
• MDR2's inability to efficiently transport MDR1 substrates may stem from impaired ATPase stimulation and reduced drug binding.
• Understanding these structural determinants can guide strategies to overcome MDR in cancer therapy.