Natural MHC Class I Polymorphism Controls the Pathway of Peptide Dissociation from HLA-B27 complexes

¹ Freie Universitaet Berlin
² Charite-Universitaetsmedizin Berlin

^* To whom correspondence should be addressed. E-mail: alexiev{at}physik.fu-berlin.de.

Submitted on September 8, 2006
Revised on October 16, 2006
Accepted on 20 April 2007

	Abstract

Analysis of antigen dissociation provides insight into peptide presentation modes of folded human leucocyte antigen (HLA) molecules, which consist of a heavy chain, ₂-microglobulin (₂m), and an antigenic peptide. Here we have monitored peptide-HLA interactions and peptide dissociation kinetics of two HLA-B27 subtypes by fluorescence depolarization techniques. A single natural amino acid substitution distinguishes the HLA-B*2705-subtype that is associated with the autoimmune disease ankylosing spondylitis (AS) from the non-disease associated HLA-B*2709 subtype. Peptides with C-terminal Arg or Lys represent 27% of the natural B*2705 ligands. Our results show that dissociation of a model peptide with a C-terminal Lys (GRFAAAIAK) follows a two-step mechanism. Final peptide release occurs in the second step for both HLA-B27 subtypes. However, thermodynamics and kinetics of peptide interactions reveal different molecular mechanisms underlying the first step, as indicated by different activation energies of 95 ± 8 kJ/mol (HLA-B*2705) and 150 ± 10 kJ/mol (HLA-B*2709). In HLA-B*2709, partial peptide dissociation probably precedes fast final peptide release, while in HLA-B*2705 an allosteric mechanisms based on long-range interactions between ₂m and the peptide binding groove controls the first step. The resulting peptide presentation mode lasts for days at physiological temperature, and determines the peptide-HLA-B*2705 conformation, which is recognized by cellular ligands such as T-cell receptors.

Key Words: HLA-complex stability, fluorescence spectroscopy, protein unfolding, thermodynamics

This article has been cited by other articles:

				D. Narzi, K. Winkler, J. Saidowsky, R. Misselwitz, A. Ziegler, R. A. Bockmann, and U. Alexiev Molecular Determinants of Major Histocompatibility Complex Class I Complex Stability: SHAPING ANTIGENIC FEATURES THROUGH SHORT AND LONG RANGE ELECTROSTATIC INTERACTIONS J. Biol. Chem., August 22, 2008; 283(34): 23093 - 23103. [Abstract] [Full Text] [PDF]