title: Evidence for involvement of a hydrophobic patch in framework region 1 of human V4-34-encoded Igs in recognition of the red blood cell I antigen.
abstract: The monoclonal IgM cold agglutinins that bind to the I/i carbohydrate Ags on the surface of RBCs all have Ig H chains encoded by the V4-34 gene segment. This mandatory use indicates that distinctive amino acid sequences may be involved in recognition. Critical amino acids exist in framework region 1 (FR1) of V4-34-encoded Ig, and these generate a specific Id determinant which apparently lies close to the I binding site. However, I binding by Id-expressing Ig can be modulated by sequences in complementarity-determining region (CDR)(H)3. Examination of the crystal structure of an anti-I cold agglutinin has revealed a hydrophobic patch in FR1 involving residue W7 on beta-strand A and the AVY motif (residues 23-25) on beta-strand B. In this study we used mutagenesis to show that each of the strand components of the hydrophobic patch is required for binding the I carbohydrate Ag. In addition, the crystal structure reveals that amino acids in the carboxyl-terminal region of CDR(H)3 form a surface region adjacent to the hydrophobic patch. We propose that the I carbohydrate Ag interacts simultaneously with the entire hydrophobic patch in FR1 and with the outside surface of CDR(H)3. This interaction could leave most of the conventional binding site available for binding other Ags.
authors.affiliation: Molecular Immunology Group, Tenovus Laboratory, Southampton University Hospitals Trust, Southampton, United Kingdom. kp1@soton.ac.uk
authors.forename: Kathleen N
authors.initials: KN
authors.lastname: Potter
authors.forename: Paul
authors.initials: P
authors.lastname: Hobby
authors.forename: Susanne
authors.initials: S
authors.lastname: Klijn
authors.forename: Freda K
authors.initials: FK
authors.lastname: Stevenson
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Sutton
mesh_terms: D000373:Agglutinins / Q000378:metabolism; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics / Q000276:immunology; D000911:Antibodies, Monoclonal / Q000235:genetics / Q000378:metabolism; D001666:Binding Sites, Antibody / Q000235:genetics; D002461:Cell Line, Transformed; D022801:Complementarity Determining Regions / Q000737:chemistry / Q000378:metabolism; D003450:Cryoglobulins; D006028:Glycosphingolipids / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007143:Immunoglobulin Heavy Chains / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007130:Immunoglobulin Idiotypes / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D007135:Immunoglobulin Variable Region / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000235:genetics; D014364:Tryptophan / Q000235:genetics
chemical_list: D000373:Agglutinins; D000911:Antibodies, Monoclonal; D022801:Complementarity Determining Regions; D003450:Cryoglobulins; D006028:Glycosphingolipids; C078965:I-antigen; D007143:Immunoglobulin Heavy Chains; D007130:Immunoglobulin Idiotypes; D007135:Immunoglobulin Variable Region; D011994:Recombinant Proteins; C029443:cold agglutinins; D012694:Serine; D014364:Tryptophan