Tumor-acquired somatic mutation affects conformation to abolish ABCG2-mediated drug resistance

Area of Science:

• Biochemistry
• Molecular Biology
• Pharmacology

Background:

• ATP-binding cassette transporter ABCG2 influences drug absorption and distribution.
• ABCG2 mediates cellular resistance to various chemotherapeutic agents.
• Somatic mutations in conserved amino acids of ABCG2 can reveal transport mechanisms.

Purpose of the Study:

• To investigate the functional impact of a tumor-derived somatic mutation (Q393K) in the conserved amino acid residue of ABCG2.
• To elucidate the molecular mechanism by which the Q393K mutation affects ABCG2 transporter function and drug resistance.

Main Methods:

• Identification of a tumor-derived somatic mutation (Q393K) in ABCG2.
• Assessment of the mutant's localization, substrate, and nucleotide interactions.
• Utilizing a conformationally sensitive antibody to evaluate transporter conformation.
• Employing structural modeling and molecular dynamics simulations based on cryo-EM structures.

Main Results:

• The Q393K mutation in ABCG2 appears incapable of conferring drug resistance despite proper localization and substrate/nucleotide interaction.
• A conformationally sensitive antibody indicated the mutant is 'locked' in a non-functional conformation.
• Structural modeling and simulations revealed the Q393K mutation forms a salt bridge with E446, stabilizing an inward-facing conformation.
• This stabilization impairs transporter flexibility and disrupts communication between substrate binding and transport.

Conclusions:

• The Q393K mutation disrupts ABCG2 function by stabilizing an inward-facing conformation, preventing conformational flexibility necessary for transport.
• This study provides molecular insights into how specific mutations can impair transporter activity, impacting drug resistance.
• Understanding these mechanisms can inform strategies for cancer therapy and drug development.