Research background
RYPRLFGIV is the second bacterial peptide identified as a cross-reactive ligand for the diabetes-derived 4C6 T-cell receptor in the study by Dolton and colleagues. It derives from enterochelin esterase of Klebsiella oxytoca, encoded by fes, an enzyme of the siderophore pathway that releases iron from ferric enterobactin and thus belongs to a conserved bacterial iron-acquisition system rather than to any pathway with an obvious link to islet biology.
The peptide was recovered, like SLPRLFPLL, by combinatorial peptide library screening against 4C6 followed by database searching for natural sequences fitting the preferred motif, and was then tested for recognition in the context of HLA-A*24:02. Its value in the panel comes from how far it diverges from the self antigen while remaining a ligand. Against preproinsulin 3-11, LWMRLLPLL, it retains the internal PRLF-containing core and a bulky aromatic residue in the second position but differs at the N-terminal anchor and across much of the C-terminal half, including a glycine and isoleucine where the self peptide carries leucines. The receptor therefore tolerates substitution at positions that conventional motif-based epitope prediction would treat as constrained, and the peptide serves as a useful outer boundary for mapping the recognition footprint.
Read together, the four sequences characterized in that work form a graded series for a single human autoreactive receptor: the weakly bound natural self peptide, a synthetic superagonist recovered by unbiased screening, and two bacterial peptides of differing similarity to the self sequence. Such series are what allow cross-reactivity to be quantified rather than asserted, and they are increasingly used to ask how much of the apparent specificity of an autoreactive T cell reflects the self antigen and how much reflects a broader recognition surface that environmental exposures can engage.
LT9751 is supplied for research use. The published recognition data are specific to the 4C6 receptor in an HLA-A*24:02 system and are not evidence of a causal role for this organism or protein in human autoimmune disease.
Research applications
- Mapping the tolerated substitution space and receptor footprint of cross-reactive T-cell recognition
- Completion of graded cross-reactivity panels spanning self, synthetic and microbial ligands
- HLA-A*24:02 multimer assembly and peptide-MHC stability measurement
- Dose-response comparison against LWMRLLPLL, QLPRLFPLL and SLPRLFPLL for a single receptor
- Evaluation of motif-based epitope prediction against experimentally confirmed divergent ligands
- Studies of bacterial iron-acquisition proteins as sources of class I ligands
References
- Dolton G, Bulek A, Wall A, et al. HLA A*24:02-restricted T cell receptors cross-recognize bacterial and preproinsulin peptides in type 1 diabetes. Journal of Clinical Investigation (2024) 134:e164535. doi:10.1172/JCI164535
- Microbial mimics supersize the pathogenic self-response. Journal of Clinical Investigation (2024), commentary. JCI 2024 commentary
- Human islet T cells are highly reactive to preproinsulin in type 1 diabetes. PNAS (2021) 118:e2107208118. doi:10.1073/pnas.2107208118
The 4C6 cross-reactivity panel and related peptides
For research use only. Not for use in diagnostic or therapeutic procedures, or for human or veterinary use.
