Project description:Alphaviruses are arthropod-borne viruses that represent a significant threat to public health at a global level. While the formation of alphaviral nucleocapsid cores, consisting of cargo nucleic acid and the viral capsid protein, is an essential molecular process of infection, the precise interactions between the two partners are ill-defined. A CLIP-seq approach was used to screen for candidate sites of interaction between the viral Capsid protein and genomic RNA of Sindbis virus (SINV), a model alphavirus. The data presented in this report indicates that the SINV capsid protein binds to specific viral RNA sequences in the cytoplasm of infected cells, but its interaction with genomic RNA in mature extracellular viral particles is largely non-specific in terms of nucleotide sequence. Mutational analyses of the cytoplasmic viral RNA-capsid interaction sites revealed a functional role for capsid binding early in infection. Interaction site mutants exhibited decreased viral growth kinetics; however, this defect was not a function of decreased particle production. Rather mutation of the cytoplasmic capsid-RNA interaction sites negatively affected the functional capacity of the incoming viral genomic RNAs leading to decreased infectivity. Furthermore, cytoplasmic capsid interaction site mutants are attenuated in a murine model of neurotropic alphavirus infection. Collectively, the findings of this study indicate that the identified cytoplasmic interactions of the viral capsid protein and genomic RNA, while not essential for particle formation, are necessary for genomic RNA function early during infection. This previously unappreciated role of capsid protein during the alphaviral replication cycle also constitutes a novel virulence determinant.
Project description:The recent outbreaks of Zika virus (ZIKV) and its association with birth defects known as Congenital Zika Syndrome warrant investigation on the molecular processes related to its infection and pathogenesis. Among the flavivirus family, only ZIKV is linked to microcephaly as announced by World Health Organization, suggesting uniqueness of ZIKV infection compared to other members. By analyzing the ZIKV-host interactome, we found that the key microRNA (miRNA) processing enzyme Dicer was a leading target of ZIKV capsid protein in neural stem cells (NSCs), and its deficiency facilitated ZIKV infection. Mechanistically, ZIKV capsid can directly interact with Dicer and block its ribonuclease activity, dampening the production of host miRNAs that are essential for neurogenesis. Interestingly, this capsid-mediated immune evasion is specific to ZIKV because capsid proteins from other close flaviviruses, e.g., dengue, yellow fever and West Nile viruses, cannot bind to Dicer or inhibit its function. By molecular mapping, we defined a ZIKV capsid H41R mutant with loss of interaction to Dicer and no longer affecting its activity. More importantly, ZIKV H41R mutant exerted almost no impact on neurogenesis in vitro when expressed in NSCs compared to wild type capsid, and in utero infection of recombinant ZIKV-H41R mutant virus resulted in less inhibition on corticogenesis than wild-type ZIKV in mouse embryos. Interestingly, the epidemic ZIKV strain reinforces the capsid-Dicer interaction by two amino acid substitution compared to ancient Africa strain. Thus, our study demonstrated that capsid-dependent suppression of Dicer function is a unique determinant of ZIKV immune evasion and pathogenesis, which may unveil a new mechanism for ZIKV-mediated microcephaly.
Project description:<p>Tick-borne encephalitis virus is an enveloped, pathogenic, RNA virus in the family Flaviviridae, genus Flavivirus. Viral particles are formed when the nucleocapsid, consisting of an RNA genome and multiple copies of the capsid protein, buds through the endoplasmic reticulum membrane and acquires the viral envelope and the associated proteins. The coordination of the nucleocapsid components to the sites of assembly and budding are poorly understood. Here, we investigate nucleocapsid assembly by characterizing the interactions of the wild-type and truncated capsid proteins with membranes by using biophysical methods and model membrane systems. We show that capsid protein initially binds membranes via electrostatic interactions with negatively-charged lipids which is followed by membrane insertion. Additionally, we show that membrane-bound capsid protein can recruit viral genomic RNA. We confirm the biological relevance of the biophysical findings by using mass spectrometry to show that purified virions contain negatively-charged lipids. Our results suggest that nucleocapsid assembly is coordinated by negatively-charged membrane patches on the endoplasmic reticulum and that the capsid protein mediates direct contacts between the nucleocapsid and the membrane.</p>
Project description:Dengue virus (DENV) and Zika virus (ZIKV) are single-stranded (+)-sense RNA viruses that infect humans and mosquitoes, posing a significant health risk in tropical and subtropical regions. Mature virions are composed of an icosahedral shell of envelope (E) and membrane (M) proteins circumscribing a lipid bilayer, which in turn contains a complex of the approximately 11 kb genomic RNA with capsid (C) proteins. Whereas the structure of the envelope is clearly defined, the structure of the packaged genome in complex with C proteins remains elusive. Here, we investigate the interactions of C proteins with viral RNA, in solution and inside mature virions, via footprinting and cross-linking experiments. We demonstrate that C protein interactions with DENV and ZIKV genomes saturate at an RNA:C protein ratio below 1:250, and that binding site lengths on the genome exhibit a bimodal distribution, suggesting that RNA-C protein complexes occur in singlets or pairs. We show that interaction sites are preferentially sites with low base pairing, as measured by previously measured SHAPE reactivity indicating structuredness. We found no preference for specific sequence motifs or nucleotide composition. However, RNA-C protein binding sites are strongly associated with long-range RNA-RNA interaction sites, particularly inside virions. This helps to explain the need of C protein for viral genome packaging: the protein could coordinate those key interactions, promoting proper packing of viral RNA. Such sites are thus possible targets for drug development strategies against these and related viruses.
Project description:The purpose of this study is to compare the gene profiles of chikungunya virus (CHIKV) capsid transfected and CHIKV infected Huh7 cells to identify the genes differentially expressed in the presence of the capsid protein during CHIKV infection