Peptide analysis, stability studies, and structural modeling explain contradictory peptide motifs and unique properties of the NOD mouse MHC class II molecule H2-A(g7).
The MHC class II molecule H2-A(g7) is the chief genetic determinant in insulin-dependent diabetes mellitus of the non-obese diabetic (NOD) mice. Poor peptide binding ability, as well as presentation of a unique subset of peptides by this molecule was suggested to promote autoimmunity in this strain. However, several laboratories have presented results in favor of an H2-A(g7) molecule that can avidly bind many different peptides. The crystal structures of H2-A(g7) in complex with two different peptides did not completely resolve this issue. To analyze the peptide binding capacity and the motif requirements of H2-A(g7), we eluted natural ligands from purified H2-A(g7) molecules isolated from the H2-A(g7)-transfected M12-C3 cells. A low peptide yield dominated by a few peptide ligands was found. Pool sequencing and alignment of individual ligands on the basis of molecular modeling revealed a peptide-binding motif with basic/aliphatic/small hydrophilic amino acids at relative position 1 (p1), aliphatic amino acids at p4, Ala at p6, and acidic amino acids and Ser/Gly at p9, as well as acidic residues at p10/11. Though weak, the binding of individual ligands, as well as the importance of an acidic C-terminal residue was confirmed by peptide binding studies to isolated H2-A(g7) molecules. Furthermore, the H2-A(g7) molecule incompletely dissociated into its constituent chains in SDS-electrophoresis under nonreducing conditions. This provides additional evidence of its weak affinity for peptides, which probably arises from the combination of beta56His/beta57Ser/beta78Ala and other unique H2-A(g7) residues in contact with the antigenic peptide. These results allow a better understanding of the role of this molecule in the development of autoimmunity and the identification of epitopes relevant to diabetes.
Münz
Christian
C
Department of Immunology, Institute for Cell Biology, University of Tübingen, Tübingen, Germany.
Hofmann
Matthias
M
Yoshida
Kenji
K
Moustakas
Antonis K
AK
Kikutani
Hitoshi
H
Stevanoviç
Stefan
S
Papadopoulos
George K
GK
Rammensee
Hans-Georg
HG
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D003922:Diabetes Mellitus, Type 1 / Q000235:genetics / Q000276:immunology*; D000949:Histocompatibility Antigens Class II / Q000032:analysis / Q000737:chemistry*; D051379:Mice; D016688:Mice, Inbred NOD; D008961:Models, Structural; D008969:Molecular Sequence Data
D000949:Histocompatibility Antigens Class II; C407099:I-A g7 antigen