Structure of murine major histocompatibility complex alloantigens: identification of cysteine residues involved in two intrachain disulfide bonds of H-2K

Two disulfide bonds are present in the antigenic portion of H-2K super(b). Four of the five cysteine residues have been shown to be involved in these intrachain linkages. Isolation of the disulfide-bonded residues was accomplished by trypsin digestion of H-2K super(b) sub(p)apa)nd subsequent gel filtration of the digested material. Reduction, alkylation and further separation of each of the pairs of disulfide-bonded peptides resulted in the separation of individual cysteine-containing peptides. Sequence analysis of each of these separated peptides indicated that Cys 101 is linked to Cys 164, and Cys 203 is linked to Cys 259. Cys 121 is not involved in intramolecular disulfide linkages. The disulfide bonds found in H-2K super(b) are homologous to those found in HLA-B7 and, most probably, in H-2D super(b), H-2K super(d), H-2D super(d) and H-2L super(d). This pattern of disulfide linkages suggest that this feature is common to all major histocompatibility complex class I antigens.