Cholesterol sensing by CD81 is important for hepatitis C virus entry

Abstract

CD81 plays a role in a variety of physiological and pathological processes. Recent structural analysis of CD81 indicates that it contains an intramembrane cholesterol-binding pocket and that interaction with cholesterol may regulate a conformational switch in the extracellular domain of CD81. Therefore, CD81 possesses a potential cholesterol sensing mechanism; however, its relevance for protein function is thus far unknown. In this study we investigate CD81 cholesterol sensing in the context of its activity as a receptor for hepatitis C virus. Structure-led mutagenesis of the cholesterol-binding pocket reduced CD81-cholesterol association, but had disparate effects on HCV, both reducing and enhancing CD81 receptor activity. We reasoned that this could be explained by alterations in the consequences of cholesterol binding. To investigate this further we performed molecular dynamic simulations of CD81 with and without cholesterol; this identified an allosteric mechanism by which cholesterol binding regulates the conformation of CD81. To test this, we designed further mutations to force CD81 into either the open (cholesterol unbound) or closed (cholesterol bound) conformation. The open mutant of CD81 exhibited reduced receptor activity whereas the closed mutant was enhanced. These data are consistent with cholesterol switching CD81 between a receptor active and inactive state. CD81 interactome analysis also suggests that conformational switching may modulate the assembly of CD81-partner networks. This work furthers our understanding of the molecular mechanism of CD81 cholesterol sensing, how this relates to HCV entry and CD81’s function as a molecular scaffold; these insights are relevant to CD81’s varied roles in health and disease.

The Tetraspanin CD81 Is a Host Factor for Chikungunya Virus Replication

“…Finally, cholesterol binding is thought to change the CD81 conformation ( 54 , 87 ), thereby affecting interactions with other human proteins. Molecular modeling suggests that binding of cholesterol results in a closed CD81 ectodomain conformation, while unbound CD81 shows a more open ectodomain conformation ( 87 ). This conformational switch is thought to influence HCV entry, which depends on the ability of CD81 to bind cholesterol ( 55 , 87 ).…”

“…Molecular modeling suggests that binding of cholesterol results in a closed CD81 ectodomain conformation, while unbound CD81 shows a more open ectodomain conformation ( 87 ). This conformational switch is thought to influence HCV entry, which depends on the ability of CD81 to bind cholesterol ( 55 , 87 ). Importantly, the majority of CD81 protein interactions are mediated by the ectodomain.…”

Cholesterol plays a decisive role in tetraspanin assemblies during bilayer deformations

“…In particular, CD81 (cluster of differentiation 81), or Tspan28 33 , is involved in cell-surface assembly of the human immunodeficiency virus (HIV), the influenza A virus and the hepatitis C virus (HCV) 55 . Several studies have highlighted the affinity of CD81 for highly curved membranes 23,28,75 or its influence in membrane remodelling and deformation 17 .…”

“…Several studies have highlighted the affinity of CD81 for highly curved membranes 23,28,75 or its influence in membrane remodelling and deformation 17 . Therefore, among tetraspanins, dynamic molecular characteristics of CD81 are of major interest to understand its disease-related physiological and pathological processes 55 .…”

CD81, a new actor in the development of preeclampsia

“…In NK cells, the crosslinking of CD81 induces phosphorylation of the ezrin/radixin/moesin (ERM) protein, and CD81 colocalizes with phosphorylated ERM at the uropod, which is associated with increased cell polarization and migration toward chemoattractants 4 . With respect to the regulatory effect of CD81 on virus infection, CD81 participates in the cell-surface assembly of both human immunodeficiency virus and influenza A virus and is essential for the entry of hepatitis C virus into hepatocytes [5][6][7] .…”