Transmembrane Polar Relay Drives the Allosteric Regulation for ABCG5/G8 Sterol Transporter

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• The ATP-binding cassette (ABC) sterol transporter ABCG5/G8 facilitates cholesterol and plant sterol secretion.
• Mutations in ABCG5/G8 cause sitosterolemia, leading to sterol accumulation and atherosclerosis.
• A recent crystal structure revealed a polar relay network in the transmembrane domains of ABCG5/G8.

Purpose of the Study:

• To investigate the functional role of the transmembrane polar relay in ABCG5/G8.
• To analyze the impact of specific genetic variants on ABCG5/G8 activity.
• To establish an in vitro phenotype for loss-of-function mutations.

Main Methods:

• Utilized genetic variants (R543S, E146Q, A540F) of ABCG5/G8.
• Demonstrated and characterized sterol-coupled ATPase activity using cholesteryl hemisuccinate (CHS).
• Assessed CHS-coupled ATPase activity of wild-type and mutant ABCG5/G8.

Main Results:

• Loss-of-function mutations significantly impaired ATPase activity.
• Mutations weakened the signal transmission from the transmembrane domains.
• Variants within, in contact with, and distant from the polar relay showed impaired function.

Conclusions:

• The transmembrane polar relay is crucial for regulating ABCG5/G8 catalytic activity.
• Biochemical evidence supports the importance of the polar relay network in transporter function.
• Understanding these mechanisms can inform strategies for sitosterolemia treatment.