Survey of high-resolution archaeal virus structures.

Archaeal viruses exhibit diverse morphologies whose structures are just beginning to be explored at high-resolution. In this review, we update recent findings on archaeal structural proteins and virion architectures and place them in the biological context in which these viruses replicate. We conclude that many of the unusual structural features and dynamics of archaeal viruses aid their replication and survival in the chemically harsh environments, in which they replicate. Furthermore, we should expect to find more novel features from examining the high-resolution structures of additional archaeal viruses.

Structural perspectives of antibody-dependent enhancement of infection of dengue virus.

Dengue virus (DENV) consists of four serotypes. Sequential serotype infections can cause increased disease severity, likely due to antibody-dependent enhancement (ADE) of infection. Here, we review two recent papers showing major advancements in the understanding of the ADE mechanism for both mature and immature DENV. The surface of both mature and immature DENV contains E and another protein - M in mature and prM in immature virus. On mature DENV, the orientation of anti-E antibody with respect to the virus surface determines the antibody enhancement properties. On the immature virus, binding of anti-prM antibody aids the dissociation of pr from the fusion loop of E protein allowing virus-endosomal membrane interaction, thus overcoming the hurdle in the early step of fusion.

Refinement and Analysis of the Mature Zika Virus Cryo-EM Structure at 3.1 Å Resolution.

Among the several arthropod-borne human flaviviral diseases, the recent outbreak of Zika virus (ZIKV) has caused devastating birth defects and neurological disorders, challenging the world with another major public health concern. We report here the refined structure of the mature ZIKV at a resolution of 3.1 Å as determined by cryo-electron microscopic single-particle reconstruction. The improvement in the resolution, compared with previous enveloped virus structures, was the result of optimized virus preparation methods and data processing techniques. The glycoprotein interactions and surface properties of ZIKV were compared with other mosquito-borne flavivirus structures. The largest structural differences and sequence variations occur at the glycosylation loop associated with receptor binding. Probable drug binding pockets were identified on the viral surface. These results also provide a structural basis for the design of vaccines against ZIKV.

Bluetongue virus structure and assembly.

Bluetongue virus (BTV) is an insect-vectored emerging pathogen of wild ruminants and livestock in many parts of the world. The virion particle is a complex structure of consecutive layers of protein surrounding a genome of ten double-stranded (ds) RNA segments. BTV has been studied as a model system for large, non-enveloped dsRNA viruses. Several new techniques have been applied to define the virus-encoded enzymes required for RNA replication to provide an order for the assembly of the capsid shell and the protein sequestration required for it. Further, a reconstituted in vitro system has defined the individual steps of the assembly and packaging of the genomic RNA. These findings illuminate BTV assembly and indicate the pathways that related viruses might use to provide an informed starting point for intervention or prevention.

Diversity of tailed phages in Baltic Sea sediment: large number of siphoviruses with extremely long tails.

We present the first attempt at quantitative analysis of morphological diversity of tailed viruses obtained from marine sediments without ultracentrifugation or enrichment on specific host strains. Sandy mud samples were collected in the Gulf of Gdansk in the spring, autumn and winter. VLPs were analyzed by transmission electron microscopy. The distribution of three groups of tailed phages was similar in all seasons (Siphoviridae: 52% on average; Myoviridae: 42%; Podoviridae: 6%). 19% of siphoviruses had prolate heads. Interestingly, 11% of siphoviral particles had tails longer than 300 nm, and 6% longer than 600 nm.

Tail morphology controls DNA release in two Salmonella phages with one lipopolysaccharide receptor recognition system.

Bacteriophages use specific tail proteins to recognize host cells. It is still not understood to molecular detail how the signal is transmitted over the tail to initiate infection. We have analysed in vitro DNA ejection in long-tailed siphovirus 9NA and short-tailed podovirus P22 upon incubation with Salmonella typhimurium lipopolysaccharide (LPS). We showed for the first time that LPS alone was sufficient to elicit DNA release from a siphovirus in vitro. Crystal structure analysis revealed that both phages use similar tailspike proteins for LPS recognition. Tailspike proteins hydrolyse LPS O antigen to position the phage on the cell surface. Thus we were able to compare in vitro DNA ejection processes from two phages with different morphologies with the same receptor under identical experimental conditions. Siphovirus 9NA ejected its DNA about 30 times faster than podovirus P22. DNA ejection is under control of the conformational opening of the particle and has a similar activation barrier in 9NA and P22. Our data suggest that tail morphology influences the efficiencies of particle opening given an identical initial receptor interaction event.