Structure of the parainfluenza virus 5 F protein in its metastable, prefusion conformation

Abstract

Enveloped viruses have evolved complex glycoprotein machinery that drives the fusion of viral and cellular membranes, permitting entry of the viral genome into the cell. For the paramyxoviruses, the fusion (F) protein catalyses this membrane merger and entry step, and it has been postulated that the F protein undergoes complex refolding during this process. Here we report the crystal structure of the parainfluenza virus 5 F protein in its prefusion conformation, stabilized by the addition of a carboxy-terminal trimerization domain. The structure of the F protein shows that there are profound conformational differences between the pre- and postfusion states, involving transformations in secondary and tertiary structure. The positions and structural transitions of key parts of the fusion machinery, including the hydrophobic fusion peptide and two helical heptad repeat regions, clarify the mechanism of membrane fusion mediated by the F protein.

A Conserved Region between the Heptad Repeats of Paramyxovirus Fusion Proteins Is Critical for Proper F Protein Folding

“…These data indicate a critical role for CBF 1 in initial folding of paramyxovirus fusion proteins. A recently published structure of the prefusogenic form of the parainfluenza 5 (PIV5/SV5) F protein reveals that CBF 1 from one monomer flanks the hydrophobic fusion peptide domain from another monomer (26). Our results therefore indicate that interactions between this conserved region and the fusion peptide are critical for folding of diverse F proteins.…”

“…The conservation of amino acids throughout the family suggests that the critical role in protein folding is a conserved function of this region. The recently published prefusogenic structure of PIV5/SV5 F (26) indicates that CBF 1 interacts with the fusion peptide. As seen in Figure 9A [adapted from (26)], CBF 1 and flanking residues (purple) from one monomer of the F protein lie adjacent to the fusion peptide (orange) from another monomer, positioning consistent with our findings that this domain is critical for forming stable oligomers.…”

“…The recently published prefusogenic structure of PIV5/SV5 F (26) indicates that CBF 1 interacts with the fusion peptide. As seen in Figure 9A [adapted from (26)], CBF 1 and flanking residues (purple) from one monomer of the F protein lie adjacent to the fusion peptide (orange) from another monomer, positioning consistent with our findings that this domain is critical for forming stable oligomers. The fusion peptide region is well-defined as the domain which inserts into a target cell membrane during the initiation of fusion.…”

Structures of vesicular stomatitis virus glycoprotein: membrane fusion revisited

“…2, 4). The viral fusion proteins belonging to class I, of which the best-characterized members are the influenza virus hemagglutinin (HA) [34,35] and the fusion protein (F) of the paramyxoviruses [36,37] but which also include fusion proteins from retroviruses [38] and filoviruses [39], are organized in trimers. Each subunit (or protomer) constituting the trimer results from the proteolytic cleavage of a precursor into two fragments.…”

“…4A) and influenza virus hemagglutinin subunit 2 (HA2) (Fig. 4C) [35,37]. Particularly, the reversal of the molecule around the rigid block involves the lengthening of the central helices (that form the trimeric central core of the post-fusion conformation, thus displaying the fusion domainsthrough the PH domains -at their N-termini) and the refolding of the three carboxy-terminal segments into helices that position themselves in the grooves of the central core in an antiparallel manner to form a sixhelix bundle (Fig.…”