PMID: 21115828

Authors:

Gunther S, Schlundt A, Sticht J, Roske Y, Heinemann U, Wiesmuller KH, Jung G, Falk K, Rotzschke O, Freund C

Title:

Bidirectional binding of invariant chain peptides to an MHC class II molecule.

Journal:

Proc Natl Acad Sci U S A. 2010 Nov 29.

Abstract:

T-cell recognition of peptides bound to MHC class II (MHCII) molecules is a central event in cell-mediated adaptive immunity. The current paradigm holds that prebound class II-associated invariant chain peptides (CLIP) and all subsequent antigens maintain a canonical orientation in the MHCII binding groove. Here we provide evidence for MHCII-bound CLIP inversion. NMR spectroscopy demonstrates that the interconversion from the canonical to the inverse alignment is a dynamic process, and X-ray crystallography shows that conserved MHC residues form a hydrogen bond network with the peptide backbone in both orientations. The natural catalyst HLA-DM accelerates peptide reorientation and the exchange of either canonically or inversely bound CLIP against antigenic peptide. Thus, noncanonical MHC-CLIP displays the hallmarks of a structurally and functionally intact antigen-presenting complex.