title: Structural basis for norovirus neutralization by an HBGA blocking human IgA antibody.
abstract: Human noroviruses (HuNoVs) cause sporadic and epidemic gastroenteritis worldwide. They are classified into two major genogroups (GI and GII), with each genogroup further divided into multiple genotypes. Susceptibility to these viruses is influenced by genetically determined histo-blood group antigen (HBGA) expression. HBGAs function as cell attachment factors by binding to a surface-exposed region in the protruding (P) domain of the capsid protein. Sequence variations in this region that result in differential HBGA binding patterns and antigenicity are suggested to form a basis for strain diversification. Recent studies show that serum antibodies that block HBGA binding correlate with protection against illness. Although genogroup-dependent variation in HBGA binding specificity is structurally well characterized, an understanding of how antibodies block HBGA binding and how genotypic variations affect such blockade is lacking. Our crystallographic studies of the GI.1 P domain in complex with the Fab fragment of a human IgA monoclonal antibody (IgA 5I2) with HBGA blocking activity show that the antibody recognizes a conformational epitope formed by two surface-exposed loop clusters in the P domain. The antibody engulfs the HBGA binding site but does not affect its structural integrity. An unusual feature of the antigen recognition by IgA 5I2 is the predominant involvement of the CDR light chain 1 in contrast to the commonly observed CDR heavy chain 3, providing a unique perspective into antibody diversity in antigen recognition. Identification of the antigenic site in the P domain shows how genotypic variations might allow escape from antibody neutralization and exemplifies the interplay between antigenicity and HBGA specificity in HuNoV evolution.
authors.affiliation: The Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030.
authors.forename: Sreejesh
authors.initials: S
authors.lastname: Shanker
authors.affiliation: Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030.
authors.forename: Rita
authors.initials: R
authors.lastname: Czakó
authors.affiliation: Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232.
authors.forename: Gopal
authors.initials: G
authors.lastname: Sapparapu
authors.affiliation: Department of Pathology, Microbiology and Immunology, Vanderbilt University Medical Center, Nashville, TN 37232.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Alvarado
authors.affiliation: The Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030.
authors.forename: Maria
authors.initials: M
authors.lastname: Viskovska
authors.affiliation: Berkeley Center for Structural Biology, Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley Laboratory, Berkeley, CA 94720.
authors.forename: Banumathi
authors.initials: B
authors.lastname: Sankaran
authors.affiliation: Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030; Department of Medicine, Baylor College of Medicine, Houston, TX 77030.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Atmar
authors.affiliation: Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232; Department of Pathology, Microbiology and Immunology, Vanderbilt University Medical Center, Nashville, TN 37232.
authors.forename: James E
authors.identifier: 0000-0002-0049-1079
authors.initials: JE
authors.lastname: Crowe
authors.affiliation: Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030; Department of Medicine, Baylor College of Medicine, Houston, TX 77030 mestes@bcm.edu vprasad@bcm.edu.
authors.forename: Mary K
authors.initials: MK
authors.lastname: Estes
authors.affiliation: The Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030; Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030; mestes@bcm.edu vprasad@bcm.edu.
authors.forename: B V Venkataram
authors.initials: BV
authors.lastname: Prasad
mesh_terms: D000595:Amino Acid Sequence; D019138:Antibodies, Blocking / Q000494:pharmacology*; D000941:Antigens / Q000737:chemistry; D001789:Blood Group Antigens / Q000276:immunology*; D018360:Crystallography, X-Ray; D000939:Epitopes / Q000737:chemistry; D005838:Genotype; D006801:Humans; D007070:Immunoglobulin A / Q000378:metabolism*; D007140:Immunoglobulin Fab Fragments / Q000378:metabolism; D008958:Models, Molecular; D009500:Neutralization Tests; D029322:Norovirus / Q000187:drug effects / Q000235:genetics / Q000276:immunology*; D000072417:Protein Domains; D014764:Viral Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D019138:Antibodies, Blocking; D000941:Antigens; D001789:Blood Group Antigens; D000939:Epitopes; D007070:Immunoglobulin A; D007140:Immunoglobulin Fab Fragments; D014764:Viral Proteins
keywords: HBGA-blockade antibody; antibody neutralization; crystal structure; norovirus; viral entry