1. Structure and Function of Large Molecular Assemblies Viral Cell Fusion Erice, June 15, 2006

3. Ligand-induced nonfusogenic dissolution of a viral membrane: Vaccinia virus (Law et al., PNAS 103, 2006)

7. Entry of Enveloped Viruses Metastable fusion proteins

8. Entry of Enveloped Viruses Metastable fusion proteins

9. Entry of Enveloped Viruses Receptor- triggered fusion Metastable fusion proteins

10. Entry of Enveloped Viruses Receptor- triggered fusion (HIV, Herpes, …) Metastable fusion proteins

11. Entry of Enveloped Viruses Receptor- triggered fusion (HIV, Herpes, …) Metastable fusion proteins Receptor-mediated endocytosis

12. Entry of Enveloped Viruses Receptor- triggered fusion (HIV, Herpes, …) Metastable fusion proteins Receptor-mediated endocytosis Endosomes

13. Entry of Enveloped Viruses Receptor-mediated endocytosis Receptor- triggered fusion Low-pH- mediated fusion (Influenza virus, Flaviviruses, Alphaviruses, …) (HIV, Herpes, …) Metastable fusion proteins H+

14. Entry of Enveloped Viruses Receptor-mediated endocytosis Receptor- triggered fusion Low-pH- mediated fusion H+ (Influenza virus, Flaviviruses, Alphaviruses, …) (HIV, Herpes, …) Metastable fusion proteins H+

15. Entry of Enveloped Viruses Receptor-mediated endocytosis Receptor- triggered fusion H+ Low-pH- mediated fusion Some retroviruses require both triggers H+ (Influenza virus, Flaviviruses, Alphaviruses, …) (HIV, Herpes, …) Metastable fusion proteins

16. Morphological Types of Enveloped Viruses Icosahedral Alpha viruses Flavi viruses ‚Spiky‘; Pleomorphic Influenza viruses (ortho-, paramyxo-, retro-, filo-, rhabdo-, corona- ….viruses)

17. Viral Fusion Proteins Class I: Orthomyxoviruses (Influenza Virus Hemagglutinin), Paramyxoviruses, Retroviruses, Filoviruses, Coronaviruses Class II: Flaviviruses (Tick-borne encephalitis TBE Virus E Protein), Alphaviruses Internal Fusion Peptide Loop COO- N-terminal (N-proximal) Fusion Peptide COO-

18. Class I: Orthomyxoviruses (Influenza Virus Hemagglutinin), Paramyxoviruses, Retroviruses, Filoviruses, Coronaviruses Viral Fusion Proteins: Generation of Metastable Structures Class II: Flaviviruses (Tick-borne encephalitis TBE Virus E Protein), Alphaviruses Inactive precursor Homotrimer Metastable State Inactive Precursor Heterodimer Metastable State Post-fusion (Hairpin) Trigger Cleavage Trigger

19. Class I Fusion Class II Fusion Modis et al., 2004; Nature 427 Jardetzky and Lamb, 2004; Nature 427

20. Different Sites of Proteolytic Activation of Viral Fusion Proteins to Generate Metastable Confomation Endocytosis Endosome TGN Influenza Virus Ebola Virus SARS Virus Nipah Virus HIV Influenza Virus Flavivirus Alphavirus Site B Site A Site C H+ ER/ Golgi

21. Ilaria Capua, Italien Fowl plague: H5 or H7 (Italy 1999: H7N1)

22. Viral Fusion Proteins Class I: Orthomyxoviruses (Influenza Virus Hemagglutinin), Paramyxoviruses, Retroviruses, Filoviruses, Coronaviruses Class II: Flaviviruses (Tick-borne encephalitis TBE Virus E Protein), Alphaviruses A new class of viral fusion proteins? no cleavage activation reversible conformational changes

23. Conversion of Flavi E into Hairpin-Like Structure

24. Class I: Orthomyxoviruses (Influenza Virus Hemagglutinin), Paramyxoviruses, Retroviruses, Filoviruses, Coronaviruses Viral Fusion Proteins: Generation of Metastable Structures Class II: Flaviviruses (Tick-borne encephalitis TBE Virus E Protein), Alphaviruses Inactive PrecursorMetastable State Inactive PrecursorMetastable State Post-fusion (Hairpin) Trigger Cleavage Trigger

25. Class I and II Post-Fusion Structures Class I Class II Jahn et al., 2003 Cell 112 membrane anchor fusion peptide stem

26. Viral Cell Fusion Erice, June 15 2006

27. Influenza HA: Cleavage site as a virulence determinant H7N1 Italy 1999: Low pathogenic vs. highly pathogenic avian virus......... P E I P K G R - // - G L F.............. P E I P K G R K R K T R -//- G L F.....