title: Understanding the molecular determinants driving the immunological specificity of the protective pilus 2a backbone protein of group B streptococcus.
abstract: The pilus 2a backbone protein (BP-2a) is one of the most structurally and functionally characterized components of a potential vaccine formulation against Group B Streptococcus. It is characterized by six main immunologically distinct allelic variants, each inducing variant-specific protection. To investigate the molecular determinants driving the variant immunogenic specificity of BP-2a, in terms of single residue contributions, we generated six monoclonal antibodies against a specific protein variant based on their capability to recognize the polymerized pili structure on the bacterial surface. Three mAbs were also able to induce complement-dependent opsonophagocytosis killing of live GBS and target the same linear epitope present in the structurally defined and immunodominant domain D3 of the protein. Molecular docking between the modelled scFv antibody sequences and the BP-2a crystal structure revealed the potential role at the binding interface of some non-conserved antigen residues. Mutagenesis analysis confirmed the necessity of a perfect balance between charges, size and polarity at the binding interface to obtain specific binding of mAbs to the protein antigen for a neutralizing response.
authors.affiliation: Novartis Vaccines and Diagnostics, Siena, Italy.
authors.forename: Annalisa
authors.initials: A
authors.lastname: Nuccitelli
authors.forename: C Daniela
authors.initials: CD
authors.lastname: Rinaudo
authors.forename: Barbara
authors.initials: B
authors.lastname: Brogioni
authors.forename: Roberta
authors.initials: R
authors.lastname: Cozzi
authors.forename: Mario
authors.initials: M
authors.lastname: Ferrer-Navarro
authors.forename: Daniel
authors.initials: D
authors.lastname: Yero
authors.forename: John L
authors.initials: JL
authors.lastname: Telford
authors.forename: Guido
authors.initials: G
authors.lastname: Grandi
authors.forename: Xavier
authors.initials: X
authors.lastname: Daura
authors.forename: Martin
authors.initials: M
authors.lastname: Zacharias
authors.forename: Domenico
authors.initials: D
authors.lastname: Maione
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D001426:Bacterial Proteins / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D018604:Epitope Mapping; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010587:Phagocytosis; D017386:Sequence Homology, Amino Acid; D013292:Streptococcus agalactiae / Q000276:immunology / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D001426:Bacterial Proteins