title: The energetic basis underpinning T-cell receptor recognition of a super-bulged peptide bound to a major histocompatibility complex class I molecule.
abstract: Although the major histocompatibility complex class I (MHC-I) molecules typically bind short peptide (p) fragments (8-10 amino acids in length), longer, "bulged" peptides are often be presented by MHC-I. Such bulged pMHC-I complexes represent challenges for T-cell receptor (TCR) ligation, although the general principles underscoring the interaction between TCRs and bulged pMHC-I complexes are unclear. To address this, we have explored the energetic basis of how an immunodominant TCR (termed SB27) binds to a 13-amino acid viral peptide (LPEPLPQGQLTAY) complexed to human leukocyte antigen (HLA) B*3508. Using the crystal structure of the SB27 TCR-HLA B*3508(LPEP) complex as a guide, we undertook a comprehensive alanine-scanning mutagenesis approach at the TCR-pMHC-I interface and examined the effect of the mutations by biophysical (affinity measurements) and cellular approaches (tetramer staining). Although the structural footprint on HLA B*3508 was small, the energetic footprint was even smaller in that only two HLA B*3508 residues were critical for the TCR interaction. Instead, the energetic basis of this TCR-pMHC-I interaction was attributed to peptide-mediated interactions in which the complementarity determining region 3α and germline-encoded complementarity determining region 1β loops of the SB27 TCR played the principal role. Our findings highlight the peptide-centricity of TCR ligation toward a bulged pMHC-I complex.
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, 3800, Australia.
authors.forename: Yu Chih
authors.initials: YC
authors.lastname: Liu
authors.forename: Zhenjun
authors.initials: Z
authors.lastname: Chen
authors.forename: Scott R
authors.initials: SR
authors.lastname: Burrows
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Purcell
authors.forename: James
authors.initials: J
authors.lastname: McCluskey
authors.forename: Jamie
authors.initials: J
authors.lastname: Rossjohn
authors.forename: Stephanie
authors.initials: S
authors.lastname: Gras
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D018360:Crystallography, X-Ray; D015797:HLA-B35 Antigen / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010455:Peptides / Q000737:chemistry*; D011485:Protein Binding; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011948:Receptors, Antigen, T-Cell / Q000737:chemistry*; D020349:Surface Plasmon Resonance; D013499:Surface Properties; D013816:Thermodynamics; D014764:Viral Proteins / Q000737:chemistry
chemical_list: D015797:HLA-B35 Antigen; D010455:Peptides; D011948:Receptors, Antigen, T-Cell; D014764:Viral Proteins