The dynamic envelope of a fusion Class II virus: Prefusion stages of Semliki Forest virus revealed by electron cryomicroscopy

Shang Rung Wu, Lars Haag, Lena Hammar, Bomu Wu, Henrik Garoff, Li Xing, Kazuyoshi Murata, R. Holland Cheng

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Semliki Forest virus is among the prototypes for Class II virus fusion and targets the endosomal membrane. Fusion protein E1 and its envelope companion E2 are both anchored in the viral membrane and form an external shell with protruding spikes. In acid environments, mimicking the early endosomal milieu, surface epitopes in the virus rearrange along with exposure of the fusion loop. To visualize this transformation into a fusogenic stage, we determined the structure of the virus at gradually lower pH values. The results show that while the fusion loop is available for external interaction and the shell and stalk domains of the spike begin to deteriorate, the E1 and E2 remain in close contact in the spike head. This unexpected observation points to E1 and E2 cooperation beyond the fusion loop exposure stage and implies a more prominent role for E2 in guiding membrane close encounter than has been earlier anticipated.

Original languageEnglish (US)
Pages (from-to)6752-6762
Number of pages11
JournalJournal of Biological Chemistry
Issue number9
StatePublished - Mar 2 2007


ASJC Scopus subject areas

  • Biochemistry

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