Peptide linkage to the α-subunit of MHCII creates a stably inverted antigen presentation complex


  • A. Schlundt
  • S. Guenther
  • J. Sticht
  • M. Wieczorek
  • Y. Roske
  • U. Heinemann
  • C. Freund


  • Journal of Molecular Biology


  • J Mol Biol 423 (3): 294-302


  • Class II proteins of the Major Histocompatibility Complex (MHCII) typically present exogenous antigenic peptides to cognate T cell receptors (TCR) of T lymphocytes. The exact conformation of peptide-MHCII (pMHCII) complexes can vary depending on the length, register and orientation of the bound peptide. We have recently found the self-peptide CLIP (class II-associated invariant chain peptide) to adopt a dynamic bidirectional binding mode with regard to the human MHCII HLA-DR1. We suggested that inversely-bound peptides could activate specific T cell clones in the context of autoimmunity. As a first step to prove this hypothesis, pMHC complexes restricted to either the canonical or inverted peptide orientation have to be constructed. Here, we show that genetically encoded linkage of CLIP and two other antigenic peptides to the HLA-DR1 α-chain results in stable complexes with inversely bound ligands. 2D-NMR and biophysical analyses indicate that the CLIP-bound pMHC(inv) complex displays high thermodynamic stability but still allows for the exchange against higher affine viral antigen. Complemented by comparable data on a corresponding β-chain-fused canonical HLA-DR1/CLIP complex we further show that linkage of CLIP leads to exactly the same binding mode as the corresponding unlinked constructs. We suggest that our approach constitutes a general strategy to create pMHC(inv) complexes. Such engineering is needed to create orientation-specific antibodies and raise T cells to study phenomena of autoimmunity caused by isomeric pMHCs.