Amino acid residues on the I-Ak alpha-chain required for the binding and stability of two antigenic peptides.
The class II molecules of the MHC bind processed Ag fragments (peptides) for presentation to T cells, but the role of individual MHC residues in binding these peptides has not been entirely defined. A panel of 27 mutant I-Ak transfectants was analyzed for the capacity to bind 2 unrelated peptides. The main peptides examined were hen egg lysozyme residues 48-62 and heat shock protein (hsp70) to residues 28-41. Alanine substitutions of sites in the alpha-helical region of the I-Ak alpha-chain altered the ability of this class II protein to bind both peptides. Of the 27 substitutions tested, nine caused a decrease in peptide binding while only three caused an increase in peptide binding. The stabilities of these altered I-Ak-peptide complexes were also examined on SDS-Page. Complexes with lowered stabilities were observed after only four substitutions, and in all four cases this loss of stability was accompanied by a loss in hen egg lysozyme or hsp70 peptide-binding ability. Further, three of these residues lie in the short extended strand at the N terminus of the alpha-helix of the alpha 1 domain, suggesting that this region of I-Ak molecule may be critical for the formation of stable peptide-MHC complexes.
Nelson
C A
CA
Department of Pathology, Washington University School of Medicine, St. Louis, MO 63110, USA.
Viner
N
N
Young
S
S
Petzold
S
S
Benoist
C
C
Mathis
D
D
Unanue
E R
ER
D000409:Alanine / Q000737:chemistry / Q000235:genetics; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D000818:Animals; D001120:Arginine / Q000737:chemistry / Q000235:genetics; D000939:Epitopes / Q000737:chemistry* / Q000235:genetics; D000949:Histocompatibility Antigens Class II / Q000737:chemistry* / Q000235:genetics; D007739:L Cells; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D011485:Protein Binding; D017433:Protein Structure, Secondary
D000596:Amino Acids; D000939:Epitopes; D000949:Histocompatibility Antigens Class II; D010446:Peptide Fragments; D001120:Arginine; D000409:Alanine