Two-dimensional nuclear magnetic resonance analysis of a labeled peptide bound to a class II major histocompatibility complex molecule.
The formation of peptide/major histocompatibility complex (MHC) complexes and their subsequent recognition by T cells is a pivotal event in the initiation of an immune response. While X-ray crystal structures are now available for class I MHC/peptide complexes, little detailed structural information is known about the class II MHC equivalent, and there are no solution structure data for either. A 16 amino acid residue moth cytochrome c peptide (residues 88 to 103) was 13C-labeled for two-dimensional isotope-edited NMR analysis. The peptide was labeled either selectively in the methyl groups of alanine residues or uniformly at every carbon position, and bound to unlabeled soluble mouse I-Ek class II MHC molecules. Although alpha-helical in the native cytochrome c protein and with no uniform structure in solution, the peptide is bound to the I-Ek molecule with the alpha-carbon atoms of the 11 C-terminal residues held in the binding groove. This indicates that the class II MHC peptide binding site is somewhat larger than that of class I MHC molecules (> or = 11 amino acid residues versus 8 to 10 amino acid residues), consistent with recent data on eluted peptides. Despite the large size of the complex (approximately 70 kDa), nuclear Overhauser effects are clearly detectable between peptide side-chains and the MHC molecule. Indications of the buried or exposed nature of particular side-chains within the bound peptide are derived from the NMR data and these are used together with information from previous biological studies to propose a crude model of the interaction of the peptide with the groove of the MHC molecule. We find no evidence for a conformational change in the peptide/MHC complex in the spectra at pH 5.0 versus pH 7.0, despite a 40-fold faster on-rate for the peptide at the lower pH value.
Department of Biochemistry Oxford University, U.K.
P C
PC
Driscoll
J D
JD
Altman
J J
JJ
Boniface
K
K
Sakaguchi
P A
PA
Reay
J G
JG
Omichinski
E
E
Appella
M M
MM
Davis
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003574:Cytochrome c Group / Q000737:chemistry*; D005805:Genes, MHC Class I; D005802:Genes, MHC Class II; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D008969:Molecular Sequence Data; D009036:Moths; D010446:Peptide Fragments / Q000737:chemistry*; D011487:Protein Conformation
D003574:Cytochrome c Group; D010446:Peptide Fragments