Structural Changes in Dengue Virus When Exposed to a Temperature of 37°C

Abstract

Previous binding studies of antibodies that recognized a partially or fully hidden epitope suggest that insect cell-derived dengue virus undergoes structural changes at an elevated temperature. This was confirmed by our cryo-electron microscopy images of dengue virus incubated at 37°C, where viruses change their surface from smooth to rough. Here we present the cryo-electron microscopy structures of dengue virus at 37°C. Image analysis showed four classes of particles. The three-dimensional (3D) map of one of these classes, representing half of the imaged virus population, shows that the E protein shell has expanded and there is a hole at the 3-fold vertices. Fitting E protein structures into the map suggests that all of the interdimeric and some intradimeric E protein interactions are weakened. The accessibility of some previously found cryptic epitopes on this class of particles is discussed. Dengue virus (DENV) is a mosquito-borne pathogen and the causative agent of dengue fever, dengue hemorrhagic fever (DHF), and the life-threatening dengue shock syndrome (DSS). Currently, DENV infects about 50 to 100 million people per year, resulting in 250,000 to 500,000 cases of DHF or DSS, making it a major health, social, and economic problem (1). This virus belongs to the family Flaviviridae, which also includes other major human pathogens, such as yellow fever virus, West Nile virus (WNV), tick-borne encephalitis virus, Japanese encephalitis virus, etc. The four DENV serotypes share high genetic homology, varying in amino acid sequence by about 25 to 40%. Genotypes within a serotype are even more conserved, containing about only 3% variation in amino acid sequence (2, 3).Envelope (E) protein is the major antigenic structure on the surface of DENV (4). Crystal structures of the ectodomain of the E protein showed that it consists of three domains (I, II, and III) and that E proteins likely exist as dimers in solution (5-7). Domain III participates in receptor binding, while domain II facilitates virus fusion via the interaction of its fusion loop at the tip of the domain with the endosomal membrane during virus entry into the cell (4). Cryo-electron microscopy (cryo-EM) structures (8, 9) of the mature DENV showed that the surface of the virus is made from 180 copies of E and 180 copies of membrane (M) proteins that are arranged in an icosahedral manner. There are three individual E proteins in each of the 60 asymmetric units (molecules A, B and C; also shown in Fig. 5B) (8, 9). Each of these E proteins is located close to one of the 2-, 3-, or 5-fold vertices, thereby having a different local chemical environment. The E proteins are organized as 90 head-to-tail homodimers. Three of these homodimers lie parallel to each other, forming a raft, and together with the other 29 rafts, they form a herringbone pattern on the surface of the virus.The previously published cryo-EM structures were done with DENV grown in mosquito cell lines incubated at 28 to 30°C for several days and then kept at 4°C during virus purification pr...

Recognition determinants of broadly neutralizing human antibodies against dengue viruses

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Which Dengue Vaccine Approach Is the Most Promising, and Should We Be Concerned about Enhanced Disease after Vaccination?

“…This can affect the accessibility of some antigenic sites which may be occluded in some conformations but exposed in others and explains why binding of some antibodies may be enhanced by prolonged incubation or by increased temperature 13 . A "bumpy" conformation of DENV2 has been described in which the virus particle is expanded and the interaction of the 90 E-dimers is changed relative to the standard mature virus particle which may disrupt some quaternary epitopes formed between opposing dimers 14,15 . It is interesting in this regard that the Zika virus (ZIKV) particles seem to be relatively more rigid than DENV particles 16,17 .…”