title: Mutational analysis and an alternatively spliced product of B7 defines its CD28/CTLA4-binding site on immunoglobulin C-like domain.
abstract: Costimulatory molecules B7 and B7-2 interact with T cell surface receptors CD28/CTLA4 and deliver a costimulatory signal essential for T cell growth. However, the structure basis of this interaction is not known. B7 and B7-2 are members of immunoglobulin (Ig) superfamily and their extracellular portion consists of an IgV- and IgC-like domain. Here we report that a naturally occurring, alternatively spliced form of B7 reveals that exon 3-encoded IgC domain is essential for CD28/CTLA4 binding. Mutational analysis of B7 demonstrates a critical role of several amino acids around loops between strands B and C and D and E, for binding CTLA4/CD28. These amino acids are clustered to form a single binding site centered at 201Y. A comparison of the effects of mutations on the binding of CD28 and CTLA4 reveals that CD28 and CTLA4 binds to the same site on B7. These results have important implications on the role of CTLA4 and CD28 in T cell costimulation. The structure of the CD28/CTLA4-binding site also provides valuable information for immune intervention targeted at the B7/B7-2-CD28/CTLA4 interactions.
authors.affiliation: Michael Heidelberger Division of Immunology, Department of Pathology, New York University Medical Center, New York 10016, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Guo
authors.forename: Y
authors.initials: Y
authors.lastname: Wu
authors.forename: M
authors.initials: M
authors.lastname: Zhao
authors.forename: X P
authors.initials: XP
authors.lastname: Kong
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
mesh_terms: D000069594:Abatacept; D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000378:metabolism*; D018122:B7-1 Antigen / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D051940:B7-2 Antigen; D001483:Base Sequence; D001665:Binding Sites; D018106:CD28 Antigens / Q000378:metabolism*; D016466:CHO Cells; D060908:CTLA-4 Antigen; D002461:Cell Line, Transformed; D002522:Chlorocebus aethiops; D006224:Cricetinae; D004252:DNA Mutational Analysis; D018796:Immunoconjugates; D007127:Immunoglobulin Constant Regions / Q000737:chemistry*; D008213:Lymphocyte Activation; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D008808:Mice, Inbred CBA; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016133:Polymerase Chain Reaction; D017434:Protein Structure, Tertiary; D012326:RNA Splicing; D013329:Structure-Activity Relationship
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D018122:B7-1 Antigen; D051940:B7-2 Antigen; D018106:CD28 Antigens; D060908:CTLA-4 Antigen; C497965:Cd86 protein, mouse; C556707:Ctla4 protein, mouse; D018796:Immunoconjugates; D007127:Immunoglobulin Constant Regions; D008562:Membrane Glycoproteins; D000069594:Abatacept