Dengue Virus Capsid Protein Binding to Hepatic Lipid Droplets (LD) Is Potassium Ion Dependent and Is Mediated by LD Surface Proteins

• Published in: Journal of Virology 2012-02, Vol.86 (4), p.2096-2108
• Main Authors: Carvalho, Filomena A, Carneiro, Fabiana A, Martins, Ivo C, Assunção-Miranda, Iranaia, Faustino, André F, Pereira, Renata M, Bozza, Patricia T, Castanho, Miguel A. R. B, Mohana-Borges, Ronaldo, Da Poian, Andrea T, Santos, Nuno C
• Format: Article
• Language: English
• Subjects: antibodies; atomic force microscopy; Biological and medical sciences; capsid; Capsid Proteins - genetics; Capsid Proteins - metabolism; coat proteins; Dengue - metabolism; Dengue - virology; Dengue virus; Dengue Virus - genetics; Dengue Virus - metabolism; dissociation; droplets; Fundamental and applied biological sciences. Psychology; Hep G2 Cells; Humans; ions; Lipid Metabolism; lipids; liver; Liver - metabolism; Liver - virology; Membrane Proteins - metabolism; Microbiology; Miscellaneous; potassium; Potassium - metabolism; Protein Binding; proteolysis; RNA; sodium; spectroscopy; surface proteins; titration; Virology; virus replication; Virus-Cell Interactions; viruses
• ISSN: 0022-538X; 1098-5514
• DOI: 10.1128/JVI.06796-11

Dengue virus (DENV) affects millions of people, causing more than 20,000 deaths annually. No effective treatment for the disease caused by DENV infection is currently available, partially due to the lack of knowledge on the basic aspects of the viral life cycle, including the molecular basis of the interaction between viral components and cellular compartments. Here, we characterized the properties of the interaction between the DENV capsid (C) protein and hepatic lipid droplets (LDs), which was recently shown to be essential for the virus replication cycle. Zeta potential analysis revealed a negative surface charge of LDs, with an average surface charge of –19 mV. The titration of LDs with C protein led to an increase of the surface charge, which reached a plateau at +13.7 mV, suggesting that the viral protein-LD interaction exposes the protein cationic surface to the aqueous environment. Atomic force microscopy (AFM)-based force spectroscopy measurements were performed by using C protein-functionalized AFM tips. The C protein-LD interaction was found to be strong, with a single (un)binding force of 33.6 pN. This binding was dependent on high intracellular concentrations of potassium ions but not sodium. The inhibition of Na+/K+-ATPase in DENV-infected cells resulted in the dissociation of C protein from LDs and a 50-fold inhibition of infectious virus production but not of RNA replication, indicating a biological relevance for the potassium-dependent interaction. Limited proteolysis of the LD surface impaired the C protein-LD interaction, and force measurements in the presence of specific antibodies indicated that perilipin 3 (TIP47) is the major DENV C protein ligand on the surface of LDs.