title: Mapping Antigenic Epitopes on the Human Bocavirus Capsid.
abstract: Human bocaviruses (HBoV1 to -4) are emerging pathogens associated with pneumonia and/or diarrhea in young children. Currently, there is no treatment or vaccination, so there is a need to study these pathogens to understand their disease mechanisms on a molecular and structural level for the development of control strategies. Here, we report the structures of six HBoV monoclonal antibody (MAb) fragment complexes, HBoV1-15C6, HBoV2-15C6, HBoV4-15C6, HBoV1-4C2, HBoV1-9G12, and HBoV1-12C1, determined by cryo-electron microscopy and three-dimensional image reconstruction to 18.0- to 8.5-Å resolution. Of these, the 15C6 MAb cross-reacted with HBoV1, HBoV2, and HBoV4, while the 4C2, 12C1, and 9G12 MAbs recognized only HBoV1. Pseudoatomic modeling mapped the 15C6 footprint to the capsid surface DE and HI loops, at the 5-fold axis and the depression surrounding it, respectively, which are conserved motifs in Parvoviridae The footprints for 4C2, 12C1, and 9G12 span the surface loops that assemble portions of the 2-/5-fold wall (a raised surface feature between the 2-fold and 5-fold axes of symmetry) and the shoulder of the 3-fold protrusions. The MAb footprints, cross reactive and strain specific, coincide with regions with high and low sequence/structural identities, respectively, on the capsid surfaces of the HBoVs and identify potential regions for the development of peptide vaccines for these viruses.
  
  
  OBJECTIVE
  Human bocaviruses (HBoVs) may cause severe respiratory and gastrointestinal infections in young children. The nonenveloped parvovirus capsid carries determinants of host and tissue tropism, pathogenicity, genome packaging, assembly, and antigenicity important for virus infection. This information is currently unavailable for the HBoVs and other bocaparvoviruses. This study identifies three strain-specific antigenic epitopes on the HBoV1 capsid and a cross-reactive epitope on the HBoV1, HBoV2, and HBoV4 capsids using structures of capsid-antibody complexes determined using cryo-electron microscopy and image reconstruction. This is the first study to report the highly conserved parvovirus DE loop at the 5-fold axis as a determinant of antigenicity. Additionally, knowledge of the strain-specific and conserved antigenic epitopes of the bocaviruses can be instrumental in characterization of the virus life cycle, development of peptide vaccines, and generation of gene delivery vectors for cystic fibrosis given the strict tropism of HBoV1 for human airway epithelial cells.
authors.affiliation: Department of Biochemistry and Molecular Biology, McKnight Brain Institute, University of Florida, Gainesville, Florida, USA.
authors.forename: Shweta
authors.initials: S
authors.lastname: Kailasan
authors.affiliation: Department of Biochemistry and Molecular Biology, McKnight Brain Institute, University of Florida, Gainesville, Florida, USA.
authors.forename: Jamie
authors.initials: J
authors.lastname: Garrison
authors.affiliation: Department of Biochemistry and Molecular Biology, McKnight Brain Institute, University of Florida, Gainesville, Florida, USA.
authors.forename: Maria
authors.initials: M
authors.lastname: Ilyas
authors.affiliation: Department of Biochemistry and Molecular Biology, McKnight Brain Institute, University of Florida, Gainesville, Florida, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Chipman
authors.affiliation: Department of Biochemistry and Molecular Biology, McKnight Brain Institute, University of Florida, Gainesville, Florida, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: McKenna
authors.affiliation: Department of Virology, University of Helsinki, Helsinki, Finland.
authors.forename: Kalle
authors.initials: K
authors.lastname: Kantola
authors.affiliation: Department of Virology, University of Helsinki, Helsinki, Finland.
authors.forename: Maria
authors.initials: M
authors.lastname: Söderlund-Venermo
authors.affiliation: Department of Immunology and Cell Biology of the Institute of Biotechnology of Vilnius University, Vilnius, Lithuania.
authors.forename: Indrė
authors.initials: I
authors.lastname: Kučinskaitė-Kodzė
authors.affiliation: Department of Immunology and Cell Biology of the Institute of Biotechnology of Vilnius University, Vilnius, Lithuania.
authors.forename: Aurelija
authors.initials: A
authors.lastname: Žvirblienė
authors.affiliation: Department of Biochemistry and Molecular Biology, McKnight Brain Institute, University of Florida, Gainesville, Florida, USA mckenna@ufl.edu.
authors.forename: Mavis
authors.initials: M
authors.lastname: Agbandje-McKenna
mesh_terms: D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000276:immunology; D000914:Antibodies, Viral / Q000737:chemistry / Q000276:immunology; D000956:Antigens, Viral / Q000276:immunology*; D002213:Capsid / Q000276:immunology* / Q000648:ultrastructure; D036022:Capsid Proteins / Q000737:chemistry / Q000276:immunology*; D003429:Cross Reactions / Q000276:immunology; D020285:Cryoelectron Microscopy; D018604:Epitope Mapping / Q000379:methods; D000939:Epitopes / Q000276:immunology*; D056661:Human bocavirus / Q000276:immunology* / Q000648:ultrastructure; D006801:Humans; D021621:Imaging, Three-Dimensional; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry / Q000276:immunology; D008958:Models, Molecular; D010322:Parvoviridae Infections / Q000821:virology; D011485:Protein Binding / Q000276:immunology; D011487:Protein Conformation
chemical_list: D000911:Antibodies, Monoclonal; D000914:Antibodies, Viral; D000956:Antigens, Viral; D036022:Capsid Proteins; D000939:Epitopes; D007140:Immunoglobulin Fab Fragments