Structure of a zosuquidar and UIC2-bound human-mouse chimeric ABCB1

Area of Science:

• Structural Biology
• Biochemistry
• Pharmacology

Background:

• ABCB1 (P-glycoprotein) is a crucial ATP-binding cassette transporter involved in multidrug resistance and tissue protection.
• Understanding ABCB1's structure is vital for developing strategies to overcome multidrug resistance in cancer therapy.

Purpose of the Study:

• To determine the near-atomic resolution cryo-EM structure of nucleotide-free ABCB1.
• To visualize the binding of the inhibitor zosuquidar and the antibody UIC2 to ABCB1.
• To elucidate the structural basis for ABCB1 inhibition and substrate efflux.

Main Methods:

• Cryo-electron microscopy (cryo-EM) at near-atomic resolution.
• Engineered disulfide cross-link to trap nucleotide-free ABCB1.
• Co-crystallization with UIC2 antibody fragment and zosuquidar inhibitor.

Main Results:

• The structure reveals an occluded ABCB1 conformation with a central, enclosed inhibitor-binding pocket.
• Two zosuquidar molecules were found within the pocket, spanning the lipid membrane.
• The binding site for the inhibitory antibody UIC2 was identified, explaining its mechanism.

Conclusions:

• The study defines the structural basis of ABCB1 inhibition by zosuquidar and UIC2.
• Distinct recognition interfaces for ABCB1 inhibitory agents were identified.
• These findings may guide the development of novel therapeutic strategies targeting ABCB1.