Structure of the thermally stable Zika virus

Abstract

Zika virus (ZIKV), formerly a neglected pathogen, has recently been associated with microcephaly in fetuses 1 , and with Guillian-Barré syndrome in adults 2 . Here we present the 3.7 Å resolution cryoelectron microscopy structure of ZIKV, and show that the overall architecture of the virus is similar to that of other flaviviruses. Sequence and structural comparisons of the ZIKV envelope (E) protein with other flaviviruses show that parts of the E protein closely resemble the neurovirulent West Nile and Japanese encephalitis viruses, while others are similar to dengue virus (DENV). However, the contribution of the E protein to flavivirus pathobiology is currently not understood. The virus particle was observed to be structurally stable even when incubated at 40 °C, in sharp contrast to the less thermally stable DENV 3 . This is also reflected in the infectivity of ZIKV compared to DENV serotypes 2 and 4 (DENV2 and DENV4) at different temperatures. The cryoelectron microscopy structure shows a virus with a more compact surface. This structural stability of the virus may help it to survive in the harsh conditions of semen 4 , saliva 5 and urine 6 . Antibodies or drugs that destabilize the structure may help to reduce the disease outcome or limit the spread of the virus.Zika virus (ZIKV), a flavivirus, is thought to be principally transmitted to humans by the mosquito (Aedes aegypti) vector. Other flaviviriuses include West Nile virus (WNV), Japanese encephalitis virus (JEV), dengue virus (DENV) and yellow fever virus (YFV). ZIKV generally causes a mild disease. However, when pregnant women are infected with ZIKV, there is an increased risk of developing microcephaly in the fetus 1 .Retrospective analysis of data collected from a ZIKV outbreak in French Polynesia in 2013-2014 showed association of the virus with microcephaly 7 . Here we present the 3.7 Å resolution structure of ZIKV strain H/PF/2013 isolated during that outbreak 8 .For cryo-electron microscopy (cryoEM) studies, ZIKV was grown in the mosquito cell line at 28 °C and purified at 4 °C by polyethylene glycol precipitation, a sucrose cushion, followed by a potassium tartrate gradient. The gel analysis of the purified sample suggested it contained mostly mature virus (Extended Data Fig. 1). The ZIKV samples were incubated at 28 °C, 37 °C and 40 °C (mimicking high fever) for 30 min, before imaging by cryoEM (Fig. 1a). At 28 °C, there were broken and shrivelled particles together with some smooth surfaced particles (about 500 Å in diameter), similar to the compact DENV mature particles. Conversely, samples incubated at 37 °C and 40 °C showed many more smooth surfaced particles. The presence of a larger fraction of shrivelled particles at 28 °C could be due to the exposure of particles to high osmolality during purification. We speculate that ZIKV particles may expand into smooth surfaced particles when incubated at higher temperatures, making the lipid envelope more fluid, and allowing the structure to revert to its normal state. Some strains of DENV2 (New G...

Structural basis of potent Zika–dengue virus antibody cross-neutralization

“…The observation that P6B10 and other FLE antibodies still neutralize DENV 13 suggests that E in the mature patches on DENV spends more time in conformations that expose the FLE than does E in those patches on ZIKV. This inference is consistent with the higher thermal stability of ZIKV reported recently 4 .…”

“…This malleability may reflect the conformational breathing reported for DENV E 18 . Instead, ZIKV sE remains in a similar conformation in the absence of the interactions with the underlying stem α-helices and with the M protein (the membrane-anchored remnant of prM after furin cleavage) on the virion, in line with the higher stability of the ZIKV particles described recently 4 .…”

“…This processing is required for infectivity, and results in the loss of a large fragment of prM and reorganization of E on the virion surface. The mature particles have a smooth aspect, with 90 E dimers organized with icosahedral symmetry in a 'herringbone' pattern 2,3 .Three-dimensional cryo-electron microscopy (cryo-EM) structures of the mature ZIKV particles have recently been reported to near atomic resolution (3.8 Å) 4,5 , showing that the virus has essentially the same organization as the other flaviviruses of known structure, such as dengue virus (DENV) 3 and West Nile virus 6,7 . The E protein is about 500 amino acids long, with the 400 N-terminal residues forming the ectodomain essentially folded as β-sheets with three domains, named I, II and III, aligned in a row with domain I at the centre.…”

Características de la estructura molecular de las proteínas E del virus Zika y E1 del virus de la rubeola. Posibles implicaciones en el neurotropismo y en las alteraciones del sistema nervioso

“…La transcripción genera un polipéptido que se procesa en tres proteínas estructurales (de la cápside: C; de membrana: M, y de membrana envolvente: E) y siete proteínas no estructurales (NS1, NS2A, NS2B, NS3, NS4A, NS4B, NS5) (12). En general, los virus con envoltura se unen y entran a sus células huéspedes mediante la fusión con la membrana celular (13), utilizando un mecanismo de endocitosis y transporte por endosomas que depende en parte de la exposición a un pH bajo (13,14) y se efectúa a través de las proteínas virales de fusión de membranas, las cuales son las principales implicadas en la unión al receptor, en la fusión y en la entrada a las células del huésped (13,14).…”

“…La estructura del ZIKV se describió recientemente con base en imágenes de criomicroscopía electrónica (12,15), con las cuales fue posible detectar y caracterizar la estructura de la proteína de envoltura E del virus (ZIKV-E) unida a un anticuerpo específico (16).…”