Cholesterol sensing by CD81 is important for hepatitis C virus entry.

Area of Science:

• Molecular biology
• Virology
• Structural biology

Background:

• CD81 protein is crucial in physiological and pathological processes.
• CD81 has a cholesterol-binding pocket, suggesting a cholesterol-sensing mechanism.
• The functional relevance of CD81 cholesterol sensing is unknown.

Purpose of the Study:

• Investigate CD81 cholesterol sensing in hepatitis C virus (HCV) entry.
• Determine how cholesterol binding affects CD81's conformation and function.
• Understand CD81's role as a molecular scaffold.

Main Methods:

• Structure-led mutagenesis of the CD81 cholesterol-binding pocket.
• Molecular dynamic simulations of CD81 with and without cholesterol.
• Mutagenesis to lock CD81 in cholesterol-bound or unbound conformations.
• CD81 interactome analysis.

Main Results:

• Mutations altering cholesterol binding had mixed effects on HCV entry.
• Molecular dynamics revealed an allosteric mechanism for cholesterol-mediated conformational change.
• Forcing CD81 into a closed (cholesterol-bound) conformation enhanced HCV entry.
• Forcing CD81 into an open (cholesterol-unbound) conformation reduced HCV entry.
• Conformational switching modulates CD81-partner protein interactions.

Conclusions:

• Cholesterol binding acts as a switch, modulating CD81's active and inactive states for HCV receptor activity.
• CD81's conformational changes influence its function as a receptor and molecular scaffold.
• Insights into CD81 cholesterol sensing are relevant to HCV infection and CD81's broader roles in health and disease.