title: Molecular basis of TCR selectivity, cross-reactivity, and allelic discrimination by a bacterial superantigen: integrative functional and energetic mapping of the SpeC-Vbeta2.1 molecular interface.
abstract: Superantigens activate large fractions of T cells through unconventional interactions with both TCR beta-chain V domains (Vbetas) and MHC class II molecules. The bacterial superantigen streptococcal pyrogenic exotoxin C (SpeC) primarily stimulates human Vbeta2(+) T cells. Herein, we have analyzed the SpeC-Vbeta2.1 interaction by mutating all SpeC residues that make contact with Vbeta2.1 and have determined the energetic and functional consequences of these mutations. Our comprehensive approach, including mutagenesis, functional readouts from both bulk T cell populations, and an engineered Vbeta2.1(+) Jurkat T cell, as well as surface plasmon resonance binding analysis, has defined the SpeC "functional epitope" for TCR engagement. Although only two SpeC residues (Tyr(15) and Arg(181)) are critical for activation of virtually all human CD3(+) T cells, a larger cluster of four hot spot residues are required for interaction with Vbeta2.1. Three of these residues (Tyr(15), Phe(75), and Arg(181)) concentrate their binding energy on the CDR2 loop residue Ser(52a), a noncanonical residue insertion found only in Vbeta2 and Vbeta4 chains. Plasticity of this loop is important for recognition by SpeC. Although SpeC interacts with the Vbeta2.1 hypervariable CDR3 loop, our data indicate these contacts have little to no influence on the functional interaction with Vbeta2.1. These studies also provide a molecular basis for selectivity and cross-reactivity of SpeC-TCR recognition and reveal a degree of fine specificity in these interactions, whereby certain SpeC mutants are capable of distinguishing between different alleles of the same Vbeta domain subfamily.
authors.affiliation: Lawson Health Research Institute.
authors.forename: A K M Nur-ur
authors.initials: AK
authors.lastname: Rahman
authors.forename: Christine A
authors.initials: CA
authors.lastname: Herfst
authors.forename: Beenu
authors.initials: B
authors.lastname: Moza
authors.forename: Stephanie R
authors.initials: SR
authors.lastname: Shames
authors.forename: Luan A
authors.initials: LA
authors.lastname: Chau
authors.forename: Clara
authors.initials: C
authors.lastname: Bueno
authors.forename: Joaquín
authors.initials: J
authors.lastname: Madrenas
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Sundberg
authors.forename: John K
authors.initials: JK
authors.lastname: McCormick
mesh_terms: D000483:Alleles; D000596:Amino Acids; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D001665:Binding Sites; D002460:Cell Line; D003429:Cross Reactions / Q000276:immunology*; D000939:Epitopes; D005098:Exotoxins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D016297:Mutagenesis, Site-Directed; D025941:Protein Interaction Mapping; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000276:immunology / Q000378:metabolism*; D018089:Superantigens / Q000276:immunology*; D020349:Surface Plasmon Resonance; D037182:T-Cell Antigen Receptor Specificity
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D000939:Epitopes; D005098:Exotoxins; D016693:Receptors, Antigen, T-Cell, alpha-beta; D018089:Superantigens; C516103:T cell receptor peptide Vbeta2.1; C027951:erythrogenic toxin