Structure and selectivity in bestrophin ion channels

Area of Science:

• Structural biology
• Ion channel biophysics
• Molecular medicine

Background:

• Human bestrophin-1 (hBest1) is a calcium-activated chloride channel crucial for retinal pigment epithelium function.
• Mutations in hBest1 are linked to vitelliform macular degeneration, also known as Best disease.

Purpose of the Study:

• To determine the structure of a bacterial homolog of hBest1 (KpBest).
• To functionally characterize both KpBest and hBest1, focusing on ion selectivity and activation.
• To provide structural context for disease-causing mutations in hBest1.

Main Methods:

• X-ray crystallography to determine the KpBest structure.
• Electrophysiological analysis of wild-type and mutant KpBest and hBest1 channels.
• Homology modeling of hBest1 based on KpBest structure.

Main Results:

• KpBest forms a pentameric channel with a five-helix transmembrane pore, featuring hydrophobic gates and a cytoplasmic cavern.
• Electrophysiological studies revealed sensitive control over ion selectivity in bestrophins, including anion/cation selectivity reversal.
• Mutations at the cytoplasmic exit dramatically enhanced channel activation.
• A homology model of hBest1 highlights the positions of disease-associated mutations.

Conclusions:

• The structure of KpBest provides a template for understanding bestrophin channel architecture and function.
• Modulating ion selectivity and activation at the cytoplasmic exit offers potential therapeutic avenues for Best disease.
• Structural insights can elucidate the molecular mechanisms underlying bestrophinopathies.