Dengue virus, a member of the Flaviviridae family, has a surface composed of 180 copies each of the envelope (E) glycoprotein and the membrane (M) protein. The crystal structure of an N-terminal fragment of E has been determined and compared with a previously described structure. The primary difference between these structures is a 10°rotation about a hinge relating the fusion domain DII to domains DI and DIII. These two rigid body components were used for independent fitting of E into the cryo-electron microscopy maps of both immature and mature dengue viruses. The fitted E structures in these two particles showed a difference of 27°between the two components. Comparison of the E structure in its postfusion state with that in the immature and mature virions shows a rotation approximately around the same hinge. Flexibility of E is apparently a functional requirement for assembly and infection of flaviviruses.
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We thank Suchetana (Tuli) Mukhopadhyay for many helpful discussions, as well as Sharon Wilder and Cheryl Towell for the preparation of the manuscript. We are grateful to Narayanasamy Nandhagopal and Alan A. Simpson, as well as people working at APS BioCARS, for help in data collection. The work was supported by NIH Program Project grants to R.J.K., M.G.R., and T.S.B. (AI 55672, AI 45976).