Cryo-EM structure of ABCG5/G8 in complex with modulating antibodies

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Medicine

Background:

• ATP-binding cassette transporters ABCG5 and ABCG8 form a heterodimer essential for sterol excretion.
• This transporter plays a vital role in maintaining cholesterol homeostasis in the liver and intestine.

Purpose of the Study:

• To determine the cryo-electron microscopy (cryo-EM) structure of the ABCG5/G8 transporter complex.
• To investigate the structural basis of transporter function and the impact of antibody binding.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to resolve the structure at 3.3Å resolution.
• The study involved complexing ABCG5/G8 with Fab fragments from two monoclonal antibodies (mAb 11F4 and mAb 2E10).

Main Results:

• A unique dimer interface between the nucleotide-binding domains (NBDs) of opposing transporters was identified, featuring salt bridges involving the NPXDFXXD motif.
• mAb 11F4 was found to enhance ATPase activity, potentially by stabilizing NBD dimer formation.
• mAb 2E10 inhibited ATP hydrolysis by restricting inter-domain movement within the ABCG8 NBD.

Conclusions:

• The study provides high-resolution structural insights into the ABCG5/G8 transport cycle mechanism.
• Identified structural features and antibody interactions reveal novel epitopes for potential therapeutic interventions targeting sterol transport.