Epstein-Barr virus (EBV) causes infectious mononucleosis and is associated with epithelial-cell cancers and B cell lymphomas. An effective EBV vaccine is not available. We found that antibodies to the EBV glycoprotein gH/gL complex were the principal components in human plasma that neutralized infection of epithelial cells and that antibodies to gH/gL and gp42 contributed to B cell neutralization. Immunization of mice and nonhuman primates with nanoparticle vaccines that displayed components of the viral-fusion machinery EBV gH/gL or gH/gL/gp42 elicited antibodies that potently neutralized both epithelial-cell and B cell infection. Immune serum from nonhuman primates inhibited EBV-glycoprotein-mediated fusion of epithelial cells and B cells and targeted an epitope critical for virus-cell fusion. Therefore, unlike the leading EBV gp350 vaccine candidate, which only protects B cells from infection, these EBV nanoparticle vaccines elicit antibodies that inhibit the virus-fusion apparatus and provide cell-type-independent protection from virus infection.

Human enterovirus 71 is a picornavirus causing hand, foot, and mouth disease that may progress to fatal encephalitis in infants and small children. As of now, no cure is available for enterovirus 71 infections. Small molecule inhibitors binding into a hydrophobic pocket within capsid viral protein 1 were previously shown to effectively limit infectivity of many picornaviruses. Here we report a 3.2-Å-resolution X-ray structure of the enterovirus 71 virion complexed with the capsid-binding inhibitor WIN 51711. The inhibitor replaced the natural pocket factor within the viral protein 1 pocket without inducing any detectable rearrangements in the structure of the capsid. Furthermore, we show that the compound stabilizes enterovirus 71 virions and limits its infectivity, probably through restricting dynamics of the capsid necessary for genome release. Thus, our results provide a structural basis for development of antienterovirus 71 capsid-binding drugs.stability | virus

Bacteriophage T4 is the most well-studied member of Myoviridae, the most complex family of tailed phages. T4 assembly is divided into three independent pathways: the head, the tail and the long tail fibers. The prolate head encapsidates a 172 kbp concatemeric dsDNA genome. The 925 Å-long tail is surrounded by the contractile sheath and ends with a hexagonal baseplate. Six long tail fibers are attached to the baseplate’s periphery and are the host cell’s recognition sensors. The sheath and the baseplate undergo large conformational changes during infection. X-ray crystallography and cryo-electron microscopy have provided structural information on protein–protein and protein–nucleic acid interactions that regulate conformational changes during assembly and infection of Escherichia coli cells.

Bacteriophage T4 consists of a head for protecting its genome and a sheathed tail for inserting its genome into a host. The tail terminates with a multiprotein baseplate that changes its conformation from a "high-energy" dome-shaped to a "low-energy" star-shaped structure during infection. Although these two structures represent different minima in the total energy landscape of the baseplate assembly, as the dome-shaped structure readily changes to the star-shaped structure when the virus infects a host bacterium, the dome-shaped structure must have more energy than the star-shaped structure. Here we describe the electron microscopy structure of a 3.3-MDa in vitro-assembled star-shaped baseplate with a resolution of 3.8 Å. This structure, together with other genetic and structural data, shows why the high-energy baseplate is formed in the presence of the central hub and how the baseplate changes to the lowenergy structure, via two steps during infection. Thus, the presence of the central hub is required to initiate the assembly of metastable, high-energy structures. If the high-energy structure is formed and stabilized faster than the low-energy structure, there will be insufficient components to assemble the low-energy structure.bacteriophage T4 | cryo-EM reconstruction | baseplate assembly | conformational changes | near-atomic resolution M ost bacteriophages have a tail. At the distal end of the tail there is usually a baseplate that is decorated by some fibers (1). The baseplate initiates infection when the tail fibers bind to a host cell. Signals are transmitted from the tail fibers via the baseplate to the tail that then trigger the ejection of the phage genome from the head into the host cell through the tail tube. Two evolutionary related structures, of pyocin (2, 3) and of the type VI secretion system (4, 5), are found in bacteria as defense systems to kill competing bacteria. These structures are remarkably similar to the tail baseplate structure of bacteriophages, suggesting that tail baseplate-like structures are effective organelles for infecting bacteria (6, 7).T4 is a member of the Myoviridae family of bacteriophages. These phages have a sheath around the tail tube that contracts during infection (Fig. 1) (8). T4 has a complex baseplate that is essential for assuring a highly efficient infection mechanism (8). After recognition of an Escherichia coli host cell by some of the six long-tail fibers (LTF), the short-tail fibers (STF) that are a part of the baseplate, bind irreversibly to the cell. This process is accompanied by a large conformational change in the baseplate from a "high-energy" dome-to a "low-energy" star-shaped structure (9, 10), although each of these structures represent an energy minimum in the energy landscape of the baseplate assembly. This change triggers contraction of the tail sheath, driving the tail tube into the outer host cell membrane and further across the periplasmic space to the inner membrane. The genomic DNA is then ejected into the host's cytoplasm. Hence, the base...

Cleavage of the alphavirus precursor glycoprotein p62 into the E2 and E3 glycoproteins before assembly with the nucleocapsid is the key to producing fusion-competent mature spikes on alphaviruses. Here we present a cryo-EM, 6.8-Å resolution structure of an "immature" Chikungunya virus in which the cleavage site has been mutated to inhibit proteolysis. The spikes in the immature virus have a larger radius and are less compact than in the mature virus. Furthermore, domains B on the E2 glycoproteins have less freedom of movement in the immature virus, keeping the fusion loops protected under domain B. In addition, the nucleocapsid of the immature virus is more compact than in the mature virus, protecting a conserved ribosome-binding site in the capsid protein from exposure. These differences suggest that the posttranslational processing of the spikes and nucleocapsid is necessary to produce infectious virus.

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The tail of bacteriophage T4 undergoes large structural changes upon infection while delivering the phage genome into the host cell. The baseplate is located at the distal end of the contractile tail and plays a central role in transmitting the signal to the tail sheath that the tailfibers have been adsorbed by a host bacterium. This then triggers the sheath contraction. In order to understand the mechanism of assembly and conformational changes of the baseplate upon infection, we have determined the structure of an in vitro assembled baseplate through the three-dimensional reconstruction of cryo-electron microscopy images to a resolution of 3.8 Å from electron micrographs. The atomic structure was fitted to the baseplate structure before and after sheath contraction in order to elucidate the conformational changes that occur after bacteriophage T4 has attached itself to a cell surface. The structure was also used to investigate the protease digestion of the assembly intermediates and the mutation sites of the tail genes, resulting in a number of phenotypes.

Virus-like particles (VLPs) are noninfectious multiprotein structures that are engineered to self-assemble from viral structural proteins. Here, we developed a novel VLP-based vaccine platform utilizing VLPs from the chikungunya virus. We identified two regions within the envelope protein, a structural component of chikungunya, where foreign antigens can be inserted without compromising VLP structure. Our VLP displays 480 copious copies of an inserted antigen on the VLP surface in a highly symmetric manner and is thus capable of inducing strong immune responses against any inserted antigen. Furthermore, by mimicking the structure of the immature form of the virus, we altered our VLP's in vivo dynamics and enhanced its immunogenicity. We used the circumsporozoite protein (CSP) of the Plasmodium falciparum malaria parasite as an antigen and demonstrated that our VLP-based vaccine elicits strong immune responses against CSP in animals. The sera from immunized monkeys protected mice from malaria infection. Likewise, mice vaccinated with P. yoelii CSP-containing VLPs were protected from an infectious sporozoite challenge. Hence, our uniquely engineered VLP platform can serve as a blueprint for the development of vaccines against other pathogens and diseases.