Explore the vast range of titles available.

Previous flavivirus (dengue and Zika viruses) studies showed largely spherical particles either with smooth or bumpy surfaces. Here, we demonstrate flavivirus particles have high structural plasticity by the induction of a non-spherical morphology at elevated temperatures: the club-shaped particle (clubSP), which contains a cylindrical tail and a disc-like head. Complex formation of DENV and ZIKV with Fab C10 stabilize the viruses allowing cryoEM structural determination to ~10 Å resolution. The caterpillar-shaped (catSP) Fab C10:ZIKV complex shows Fabs locking the E protein raft structure containing three E dimers. However, compared to the original spherical structure, the rafts have rotated relative to each other. The helical tail structure of Fab C10:DENV3 clubSP showed although the Fab locked an E protein dimer, the dimers have shifted laterally. Morphological diversity, including clubSP and the previously identified bumpy and smooth-surfaced spherical particles, may help flavivirus survival and immune evasion. Dengue (DENV) and Zika (ZIKV) viruses normally display as smooth spherical particles, while DENV can also become bumpy-surfaced, resulting in immune evasion. Here, Morrone et al. report DENV and ZIKV infectious club-shaped particles (clubSP) that display distinct antibody binding properties.

About the Authors: Ter Yong Tan Affiliations Programme in Emerging Infectious Diseases, Duke–National University of Singapore Medical School, Singapore, Singapore, Centre for BioImaging Sciences, Department of Biological Sciences, National University of Singapore, Singapore, Singapore ORCID logo http://orcid.org/0000-0002-6540-7026 Guntur Fibriansah Affiliations Programme in Emerging Infectious Diseases, Duke–National University of Singapore Medical School, Singapore, Singapore, Centre for BioImaging Sciences, Department of Biological Sciences, National University of Singapore, Singapore, Singapore ORCID logo http://orcid.org/0000-0002-9990-3335 Shee-Mei Lok * E-mail: sheemei.lok@duke-nus.edu.sg Affiliations Programme in Emerging Infectious Diseases, Duke–National University of Singapore Medical School, Singapore, Singapore, Centre for BioImaging Sciences, Department of Biological Sciences, National University of Singapore, Singapore, Singapore ORCID logo http://orcid.org/0000-0003-4631-8041 Citation: Tan TY, Fibriansah G, Lok S-M (2020) Capsid protein is central to the birth of flavivirus particles. C, Capsid; cryoEM, cryo-electron microscopy; E, Envelope; ER, endoplasmic reticulum; prM, precursor Membrane; TGN, trans-Golgi network; TM, transmembrane. https://doi.org/10.1371/journal.ppat.1008542.g001 [Figure omitted. Three neighboring building blocks are shown and colored in orange, purple, and brown. asu, asymmetric unit; C, Capsid; cryoEM, cryo-electron microscopy; E, Envelope; Fab, antigen-binding fragment; ImmZIKV, immature ZIKV; prM, precursor Membrane; ZIKV, Zika virus. https://doi.org/10.1371/journal.ppat.1008542.g002 The surface protein structures prM and E of the immature and mature flavivirus particles Cryo-electron microscopy (cryoEM) structures of the immature and mature flavivirus show that their surface proteins, although they are organized in a vastly different way, both exhibit icosahedral symmetries (Fig 2A) [2–4]. During the egress of the immature virus through the acidic compartments of the trans-Golgi network, the low pH triggers the reorganization of the heterotrimeric spikes into a dimeric surface protein organization (Figs 1A–1C and 2A) [5].

Structures of flavivirus (dengue virus and Zika virus) particles are known to near-atomic resolution and show detailed structure and arrangement of their surface proteins (E and prM in immature virus or M in mature virus). By contrast, the arrangement of the capsid proteins:RNA complex, which forms the core of the particle, is poorly understood, likely due to inherent dynamics. Here, we stabilize immature Zika virus via an antibody that binds across the E and prM proteins, resulting in a subnanometer resolution structure of capsid proteins within the virus particle. Fitting of the capsid protein into densities shows the presence of a helix previously thought to be removed via proteolysis. This structure illuminates capsid protein quaternary organization, including its orientation relative to the lipid membrane and the genomic RNA, and its interactions with the transmembrane regions of the surface proteins. Results show the capsid protein plays a central role in the flavivirus assembly process. The structure of flavivirus surface proteins has been elucidated, but the conformation of capsid proteins within particles is less clear. Here, the authors provide a subnanometer resolution structure of Zika virus capsid protein within the virus particle, elucidating its quaternary organization and role in flavivirus packaging.

AimWe assessed the feasibility of storing sera in primary gel separator tube over medium-term for retrospective serological tests to facilitate investigation of intra-uterine infection.Method120 residual serum samples, consisting of 30 positive samples each for rubella, cytomegalovirus, parvovirus B19 and varicella zoster IgG were aliquoted into secondary propylene tubes and stored together with the original primary tubes at −20°C for 1 year. The serum was subsequently retested to compare results from both storage methods.ResultsHaemolysis was observed in 49.2% of serum stored in the primary tubes. However, there was no difference in both the qualitative and quantitative results after storage of serum samples in either receptacle.ConclusionSera can be stored in primary blood tube for up to 1 year without affecting serological results. For laboratories with adequate freezer space to store samples in primary blood tubes, this would streamline workflow saving manpower and time, avoid mislabelling of aliquots, reduce consumable costs and prevent unnecessary biohazard exposures.

The rapid spread of Zika virus (ZIKV), which causes microcephaly and Guillain-Barré syndrome, signals an urgency to identify therapeutics. Recent efforts to rescreen dengue virus human antibodies for ZIKV cross-neutralization activity showed antibody C10 as one of the most potent. To investigate the ability of the antibody to block fusion, we determined the cryoEM structures of the C10-ZIKV complex at pH levels mimicking the extracellular (pH8.0), early (pH6.5) and late endosomal (pH5.0) environments. The 4.0 Å resolution pH8.0 complex structure shows that the antibody binds to E proteins residues at the intra-dimer interface, and the virus quaternary structure-dependent inter-dimer and inter-raft interfaces. At pH6.5, antibody C10 locks all virus surface E proteins, and at pH5.0, it locks the E protein raft structure, suggesting that it prevents the structural rearrangement of the E proteins during the fusion event—a vital step for infection. This suggests antibody C10 could be a good therapeutic candidate. There is a pressing need for therapeutic agents against Zika virus (ZIKV). Here the authors present cryoEM structures of a neutralizing antibody (C10) complexed with ZIKV that show C10 preventing structural changes required for virus entry into the cell, suggesting it might be effective in treating Zika infections.

Flaviviruses such as the Zika virus (ZIKV) first assemble as immature virus particles that subsequently undergo maturation into infectious mature virions. Cryo-electron microscopy (CryoEM) structures of these viruses have revealed detailed structural organization of the surface glycoproteins (namely, E and prM/M proteins). However, the structure of capsid protein within the core of the virus remains unknown. Here, we stabilized the structure of immature ZIKV (ImmZIKV) with the antigen-binding fragment (Fab) of human monoclonal antibody (HMAb) DV62.5 that binds across and locks the prM and E proteins. This strategy allowed for the determination of a subnanometer resolution capsid protein shell within the immature virus particle. Model building with the ImmZIKV:Fab DV62.5 complexed map shows that three capsid dimers associate into a triangular capsid network. In addition, using mass spectrometry and in vitro cleavage assays, we show that there exist two populations of capsid proteins within the nucleocapsid of the virus. Importantly, these two species of capsid proteins differ in a C-terminal helix that was thought to be cleaved off during polyprotein processing. Collectively, these results elucidate the quaternary organization of capsid proteins within the core of ImmZIKV and highlight the important roles that capsids play in the virus assembly process.