RT Journal Article SR Electronic T1 A high resolution view of an adolescent flavivirus JF bioRxiv FD Cold Spring Harbor Laboratory SP 2020.06.07.138669 DO 10.1101/2020.06.07.138669 A1 Max Renner A1 Wanwisa Dejnirattisai A1 Loïc Carrique A1 Itziar Serna Martin A1 Dimple Karia A1 Serban L Ilca A1 Shu F Ho A1 Abhay Kotecha A1 Jeremy R Keown A1 Juthathip Mongkolsapaya A1 Gavin R. Screaton A1 Jonathan M. Grimes YR 2020 UL http://biorxiv.org/content/early/2020/06/07/2020.06.07.138669.abstract AB Mosquito-transmitted flaviviruses, such as Dengue virus (DENV) or Zika virus (ZIKV), are responsible for significant economic damage and human misery. In infected cells, flaviviruses first assemble into an immature form within the endoplasmatic reticulum (ER), and then undergo further processing by furin protease in the trans-Golgi. Despite substantial efforts, previous cryogenic electron microscopy (cryo-EM) studies of immature flaviviruses were restricted to low to medium resolutions, limiting our understanding of maturation. To better grasp the process of maturation, we have carried out cryo-EM reconstructions of immature Spondweni virus (SPOV), an emerging human flavivirus belonging to the same serogroup as ZIKV (~75% amino acid identity). By combining localized reconstruction and focused refinement, we were able to improve the resolution to 3.8 Å, yielding unprecedented insight into the immature form. The structure elucidates how, at neutral pH, polar interactions conceal the furin recognition site within trimeric envelope (E) protein spikes. Furthermore, we identify how a strictly conserved pH sensor anchors the precursor membrane (prM) protein to immature E. We reconstructed mature forms of SPONV and DENV to 2.6Å and 3.1Å, respectively. Comparison with immature virus shows a conserved binding pocket for a lipid headgroup, which forms as a consequence of the rearrangement of amphipathic stem-helices of E. We propose a structural role for the pocket and suggest it stabilizes mature E. Taken together, our data suggest a compelling rationale for low-pH triggered conformational rearrangement in the Golgi, which occurs during flavivirus maturation.Competing Interest StatementThe authors have declared no competing interest.