title: Five of Five VHHs Neutralizing Poliovirus Bind the Receptor-Binding Site.
abstract: Nanobodies, or VHHs, that recognize poliovirus type 1 have previously been selected and characterized as candidates for antiviral agents or reagents for standardization of vaccine quality control. In this study, we present high-resolution cryo-electron microscopy reconstructions of poliovirus with five neutralizing VHHs. All VHHs bind the capsid in the canyon at sites that extensively overlap the poliovirus receptor-binding site. In contrast, the interaction involves a unique (and surprisingly extensive) surface for each of the five VHHs. Five regions of the capsid were found to participate in binding with all five VHHs. Four of these five regions are known to alter during the expansion of the capsid associated with viral entry. Interestingly, binding of one of the VHHs, PVSS21E, resulted in significant changes of the capsid structure and thus seems to trap the virus in an early stage of expansion.
  
  
  OBJECTIVE
  We describe the cryo-electron microscopy structures of complexes of five neutralizing VHHs with the Mahoney strain of type 1 poliovirus at resolutions ranging from 3.8 to 6.3Å. All five VHHs bind deep in the virus canyon at similar sites that overlap extensively with the binding site for the receptor (CD155). The binding surfaces on the VHHs are surprisingly extensive, but despite the use of similar binding surfaces on the virus, the binding surface on the VHHs is unique for each VHH. In four of the five complexes, the virus remains essentially unchanged, but for the fifth there are significant changes reminiscent of but smaller in magnitude than the changes associated with cell entry, suggesting that this VHH traps the virus in a previously undescribed early intermediate state. The neutralizing mechanisms of the VHHs and their potential use as quality control agents for the end game of poliovirus eradication are discussed.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Mike
authors.initials: M
authors.lastname: Strauss
authors.affiliation: Department of Pharmaceutical Biotechnology and Molecular Biology, Center for Neurosciences, Vrije Universiteit Brussel, Brussels, Belgium Department of Clinical Chemistry and Radio-immunology, Universitair Ziekenhuis Brussel, Brussels, Belgium.
authors.forename: Lise
authors.initials: L
authors.lastname: Schotte
authors.affiliation: Department of Pharmaceutical Biotechnology and Molecular Biology, Center for Neurosciences, Vrije Universiteit Brussel, Brussels, Belgium.
authors.forename: Bert
authors.initials: B
authors.lastname: Thys
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Filman
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA james_hogle@hms.harvard.edu.
authors.forename: James M
authors.initials: JM
authors.lastname: Hogle
mesh_terms: D000595:Amino Acid Sequence; D057134:Antibodies, Neutralizing / Q000276:immunology*; D000914:Antibodies, Viral / Q000276:immunology*; D000998:Antiviral Agents / Q000276:immunology*; D001665:Binding Sites / Q000276:immunology; D002213:Capsid / Q000648:ultrastructure; D036022:Capsid Proteins / Q000276:immunology; D045744:Cell Line, Tumor; D020285:Cryoelectron Microscopy; D006367:HeLa Cells; D006801:Humans; D017955:Poliovirus / Q000276:immunology*; D011991:Receptors, Virus / Q000276:immunology*; D016415:Sequence Alignment; D061905:Single-Domain Antibodies / Q000276:immunology* / Q000648:ultrastructure
chemical_list: D057134:Antibodies, Neutralizing; D000914:Antibodies, Viral; D000998:Antiviral Agents; D036022:Capsid Proteins; D011991:Receptors, Virus; D061905:Single-Domain Antibodies; C066100:poliovirus receptor