Haptenization of ovalbumin with the skin sensitizer methyl octanesulfonate: Characterization of the methylated OVA323‐339 T‐cell epitope at His331

Our interest is focused on the induction of allergic contact dermatitis (ACD) by the strong skin sensitizer, methyl octanesulfonate, which is a potent methyl transfer agent, especially to histidine and methionine residues. We are particularly interested to study the effect of methylation on the presentation and recognition of the ovalbumin (OVA) T-cell epitope, OVA323-339, by the T-cell receptor (TCR). Here we report the synthesis of the modified monomer N-alpha-Fmoc-N-tau-methyl-L-histidine and its incorporation by solid phase synthesis into the three possible methylated analogues of OVA323-339, that were needed as references for the subsequent studies. Native OVA was haptenized by methyl octanesulfonate. Using classical protein chemistry techniques (trypsin digestion, gel permeation, HPLC, MS and Edman sequencing) we were able to show that OVA323-339 was selectively methylated at His331. Circular dichroism (CD) studies showed that the methylation has no influence on the secondary structure of the peptide.