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

Structure and Function of Large Molecular Assemblies

Viral Cell Fusion

Erice, June 15, 2006

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

Entry of Enveloped Viruses

Metastable fusion proteins

Entry of Enveloped Viruses

Metastable fusion proteins

Entry of Enveloped Viruses

Receptor-triggered fusion

Metastable fusion proteins

Entry of Enveloped Viruses

Receptor-triggered fusion

(HIV, Herpes, …)Metastable

fusion proteins

Entry of Enveloped Viruses

Receptor-triggered fusion

(HIV, Herpes, …)Metastable

fusion proteins

Receptor-mediated endocytosis

Entry of Enveloped Viruses

Receptor-triggered fusion

(HIV, Herpes, …)Metastable

fusion proteins

Receptor-mediated endocytosis

Endosomes

Entry of Enveloped Viruses

Receptor-mediated endocytosis

Receptor-triggered fusion

Low-pH-mediated fusion

(Influenza virus, Flaviviruses, Alphaviruses, …)

(HIV, Herpes, …)Metastable

fusion proteins

H+

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+

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

Morphological Types of Enveloped Viruses

Icosahedral

Alpha viruses

Flavi viruses

‚Spiky‘; Pleomorphic

Influenza viruses

(ortho-, paramyxo-, retro-, filo-, rhabdo-, corona- ….viruses)

Viral Fusion ProteinsClass 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-

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

HeterodimerMetastable State

Post-fusion (Hairpin)

Post-fusion (Hairpin)

Trigger

Cleavage

Cleavage

Trigger

Class I FusionClass I Fusion

Class II FusionClass II Fusion

Modis et al., 2004; Nature 427

Jardetzky and Lamb, 2004; Nature 427

Different Sites of Proteolytic Activationof Viral Fusion Proteins to Generate Metastable Confomation

Endocytosis

Endosome

TGN

Influenza Virus

Ebola VirusSARS VirusNipah Virus

HIVInfluenza VirusFlavivirusAlphavirus

Site B

Site ASite C

H+

ER/ Golgi

Ilaria Capua, Italien

Ilaria Capua, Italien

Fowl plague: H5 or H7

(Italy 1999: H7N1)

Viral Fusion ProteinsClass 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

Conversion of Flavi E into Hairpin-LikeStructure

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 Metastable State

Inactive Precursor Metastable State

Post-fusion (Hairpin)

Post-fusion (Hairpin)

Trigger

Cleavage

Cleavage

Trigger

Class I and II Post-Fusion StructuresClass I and II Post-Fusion Structures

Class IClass I Class IIClass II

Jahn et al., 2003Cell 112

membrane anchor

fusion peptide

stem

Viral Cell FusionViral Cell Fusion

Erice, June 15 2006

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 . . . . .