Interaction of pigeon cytochromec-(43–58) peptide analogs with either T cell antigen receptor or I-A^b molecule

Abstract

We determined that a pigeon cytochrome c-derived peptide, p43-58, possesses two anchor residues, 46 and 54, for binding with the I-A b molecule that are compatible to the position 1 (P1) and position 9 (P9) of the core region in the major histocompatibility complex (MHC) class II binding peptides, respectively. In the present study to analyze each binding site between P1 and P9 of p43-58 to either I-A b or T cell antigen receptor (TCR), we investigated T cell responses to a series of peptides (P2K, P3K, P4K, P5K, P6K, P7K, and P8E) that sequentially substituted charged amino acid residues for the residues at P2 to P8 of p43-58. T cells from C57BL͞10 (I-A b ) mice immunized with P4K or P6K did not mount appreciable proliferative responses to the immunogens, but those primed with other peptides (P2K, P3K, P5K, P7K, and P8E) showed substantial responses in an immunogenspecific manner. It was demonstrated by binding studies that P1 and P9 functioned as main anchors and P4 and P6 functioned as secondary anchors to I-A b . Analyses of V␤ usage of T cell lines specific for these analogs suggested that P8 interacts with the complementarity-determining region 1 (CDR1)͞CDR2 of the TCR ␤ chain. Furthermore, sequencing of the TCR on T cell hybridomas specific for these analogs indicated that P5 interacts with the CDR3 of the TCR ␤ chain. The present findings are consistent with the threedimensional structure of the trimolecular complex that has been reported for TCR͞peptide͞MHC class I molecules.Formation of a trimolecular complex among T cell antigen receptor (TCR), major histocompatibility complex (MHC) molecule, and peptide antigen (Ag) is essential for T cell activation (1, 2). Recently, Garcia et al. (3) and Garboczi et al. (4) crystallized 2C TCR-K b -dEV8 and TCR-HLA-A2-Tax peptide, respectively. These crystallized trimolecular complexes were shown to possess similar structures. The long dimensions of the TCR and MHC class I peptide binding surfaces are tilted approximately 20°to 30°toward the diagonal. These restrictions may place the CDR1 and CDR2 of the TCR ␤ chain over the ␤1 and ␣1 helices of the MHC class I molecule, respectively. This orientation of TCR to MHC class I peptide resembles the model of TCR-MHC class II complex proposed by Sant'Angelo et al. (5), in which the complementarity-determining region (CDR)1 and CDR2 of the TCR ␣ chain lie over the N-terminal region of the peptide, CDR3 of the TCR ␣ chain interacts with the central position (P) 5 of the peptide, and CDR3 of the TCR ␤ chain has interactions extending from P5 to P8. However, this orientation appears to differ from the model proposed by Jorgensen et al. (6), in which the TCR is rotated approximately 90°relative to the peptide-MHC surface. Thus far, no crystal structure of trimolecular complex, including class II molecules, has been determined, and it is unclear whether formation of the trimolecular complex is predicted by a general model demonstrated with a MHC class I molecule or is determined individually by each of the component...

Naturally Occurring Altered Peptide Ligands Control Salmonella-Specific CD4+ T Cell Proliferation, IFN-γ Production, and Protective Potency

“…Accordingly, the phenylalanine corresponding to residue 431 within FliC corresponds to position P1, and alanine 434 , threonine 436 , and glycine 439 correspond to positions P4, P6, and P9, respectively (Fig 1). The importance of positions P2, P3, P5, P7, and P8 for direct contact with the TCR has also been confirmed by both biochemical and crystallographic experimental approaches (31–34). In turn, residues asparagine 432 , serine 433 , isoleucine 435 , asparagine 437 , and leucine 438 within FliC 431–439 correspond to the TCR contact sites at positions P2, P3, P5, P7, and P8, respectively (Fig 1).…”

“…The peptide that spans amino acids 431–439 within FliC are presented by MHC class II I-A b as CD4 + T cells with specificity for this peptide are readily identified in naïve C57BL/6 mice and cell lines derived from these mice after stimulation with heat-killed Salmonella (25, 30). Alignment with other well-characterized I-A b peptides reveals the putative MHC class II anchor and TCR contact residues within the FliC 431–439 peptide (Fig 1) (31–34). An essential role for amino acid positions P1, P4, P6 and P9 in direct contact and anchoring the peptide to I-A b MHC has been demonstrated through mutational analysis and biochemical-binding/affinity assays (31, 32), and these results have been confirmed by the resolved crystal structure of I-A b -restricted peptides bound to this MHC molecule (33, 34).…”

“…Alignment with other well-characterized I-A b peptides reveals the putative MHC class II anchor and TCR contact residues within the FliC 431–439 peptide (Fig 1) (31–34). An essential role for amino acid positions P1, P4, P6 and P9 in direct contact and anchoring the peptide to I-A b MHC has been demonstrated through mutational analysis and biochemical-binding/affinity assays (31, 32), and these results have been confirmed by the resolved crystal structure of I-A b -restricted peptides bound to this MHC molecule (33, 34). These studies reveal amino acids containing large, hydrophobic aromatic side chains are predominantly found at position P1, while amino acids with small, uncharged side chains are frequently present at positions P4, P6 and P9.…”

Physiological Induction of Regulatory Qa-1-Restricted CD8+ T Cells Triggered by Endogenous CD4+ T Cell Responses

“…We hypothesized that the endogenous activation of Vß8.2+CD4+ T cells might trigger a protective effect similar to that induced by the vaccinating T cells during TCV. Immunization with a peptide derived from the Pigeon Cytochrome C (PCC), a model non-self antigen in our studies, induces the activation of PCC-specific CD4+ T cells belonging predominantly to the Vß8.2 family [6], [7]. We thus immunized mice with either PCC or a control peptide derived from ovalbumin (OVA) that induces a Vß5+ CD4+ T cell response.…”

Evidence for preferred MHC class II-TCR recognition independent of the source of bound peptide

“…The other [4] shows an important contact between the CDR1 g and a residue at position 8 of the peptide. There is a previous study [23] showing that a single substitution in position 8 of the presented peptide can change the responding TCR V g utilization, which would be compatible with V g chain interaction with peptide. Thus, TCR interactions are not simply compartmentalized into CDR1 + CDR2 reacting with MHC and CDR3 with peptide, as would be expected in a strict preferential interaction model.…”