Differential Cholesterol Binding by Class II Fusion Proteins Determines Membrane Fusion Properties

Abstract

The class II fusion proteins of the alphaviruses and flaviviruses mediate virus infection by driving the fusion of the virus membrane with that of the cell. These fusion proteins are triggered by low pH, and their structures are strikingly similar in both the prefusion dimer and the postfusion homotrimer conformations. Here we have compared cholesterol interactions during membrane fusion by these two groups of viruses. Using cholesteroldepleted insect cells, we showed that fusion and infection by the alphaviruses Semliki Forest virus (SFV) and Sindbis virus were strongly promoted by cholesterol, with similar sterol dependence in laboratory and field isolates and in viruses passaged in tissue culture. The E1 fusion protein from SFV bound cholesterol, as detected by labeling with photocholesterol and by cholesterol extraction studies. In contrast, fusion and infection by numerous strains of the flavivirus dengue virus (DV) and by yellow fever virus 17D were cholesterol independent, and the DV fusion protein did not show significant cholesterol binding. SFV E1 is the first virus fusion protein demonstrated to directly bind cholesterol. Taken together, our results reveal important functional differences conferred by the cholesterol-binding properties of class II fusion proteins.

Low pH-dependent Hepatitis C Virus Membrane Fusion Depends on E2 Integrity, Target Lipid Composition, and Density of Virus Particles

“…The fusion step per se of several flaviviruses is only facilitated by the presence of chol or chol/SM in the target membranes (66,77,78), whereas the presence of these lipids is a strict prerequisite for the fusion of the closely related alphaviruses. This facilitation is most likely not because of a direct binding of their envelope proteins to any of these lipids, in striking contrast to what was observed/suggested for the envelope glycoproteins of alphaviruses (76,79,80). Increasing evidence indicates that CD81-mediated HCV entry is dependent upon chol (43,81) and ceramide levels at the plasma membrane (82).…”

“…72). In the Flaviviridae family of viruses, the cellular internalization and entry of the West Nile and Dengue viruses were shown to depend on chol-enriched microdomains (73,74); along the same lines, chol depletion of the plasma membrane impaired cell entry of the Japanese encephalitis virus and the Dengue (75), although conflicting results have been reported (76). The fusion step per se of several flaviviruses is only facilitated by the presence of chol or chol/SM in the target membranes (66,77,78), whereas the presence of these lipids is a strict prerequisite for the fusion of the closely related alphaviruses.…”

Inhibition of Ebola virus glycoprotein-mediated cytotoxicity by targeting its transmembrane domain and cholesterol

“…A cholesterol gradient exists across the secretory pathway 41 (low in the endoplasmic reticulum (ER) and high in the plasma membrane), and would hence allow the formation of filaments at the plasma membrane, but not in the endomembrane system. To analyse the specific interactions of GP with cholesterol, we utilized a well-established photoaffinity-labelling assay [42][43][44][45] . Radioactively labelled (tritiated) photoactivatable cholesterol was fed to HeLa cells expressing either FLAG-GP 1,2 , FLAG-GP 2 or their respective variants.…”

Plasmablasts Generated during Repeated Dengue Infection Are Virus Glycoprotein–Specific and Bind to Multiple Virus Serotypes

“…Purified Abs were used for screening. E protein-specific Abs were measured on plates coated with 300 ng/well E protein of DENV1 or DENV3 (ProSpec-Tany TechnoGene) or 150 ng/well E protein of DENV2-TSV01, which was produced in S2 cells, as described (28). Supernatants from Abexpressing 293HEK cells or purified Abs were used for screening.…”