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J. Biol. Chem., Vol. 278, Issue 9, 7189-7198, February 28, 2003

This Article Full Text Full Text (PDF) All Versions of this Article: 278/9/7189    most recent M206015200v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hammar, L. Articles by Cheng, R. H. Search for Related Content PubMed PubMed Citation Articles by Hammar, L. Articles by Cheng, R. H. Social Bookmarking                      What's this?

Prefusion Rearrangements Resulting in Fusion Peptide Exposure in Semliki Forest Virus^*

Lena Hammar^§, Sevak Markarian, Lars Haag, Hilkka Lankinen^¶, Aimo Salmi, and R. Holland Cheng

From the  Department of Biosciences, Karolinska Institute, Huddinge S-141 57, Sweden, the ^¶ Haartman Institute, Department of Virology, Helsinki F-00014, Finland, and the  Department of Virology, University of Turku, Turku F-20520, Finland

Semliki Forest virus (SFV), like many enveloped viruses, takes advantage of the low pH in the endosome to convert into a fusion-competent configuration and complete infection by fusion with the endosomal membrane. Unlike influenza virus, carrying an N-terminal fusion peptide, SFV represents a less-well understood fusion principle involving an endosequence fusion peptide. To explore the series of events leading to a fusogenic configuration of the SFV, we exposed the virus to successive acidification, mimicking endosomal conditions, and followed structural rearrangements at probed sensor surfaces. Thus revealed, the initial phase involves a transient appearance of a non-linear neutralizing antibody epitope in the fusion protein, E1. Concurrent with the disappearance of this epitope, a set of masked sequences in proteins E1 and E2 became exposed. When pH reached 6.0-5.9 the virion transformed into a configuration of enlarged diameter with the fusion peptide optimally exposed. Simultaneously, a partly hidden sequence close to the receptor binding site in E2 became fully uncovered. At this presumably fusogenic stage, maximally 80 fusion peptide-identifying antibody Fab fragments could be bound per virion, i.e. one ligand per three copies of the fusion protein. The phenomena observed are discussed in terms of alphavirus structure and reported functional domains.

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