Natural T Cell Epitope Containing Methyl Lysines on Mycobacterial Heparin-Binding Hemagglutinin

Abstract

T cell epitopes are mostly nonmodified peptides, although posttranslationally modified peptide epitopes have been described, but they originated from viral or self-proteins. In this study, we provide evidence of a bacterial methylated T cell peptide epitope. The mycobacterial heparin-binding hemagglutinin (HBHA) is a protein Ag with a complex C-terminal methylation pattern and is recognized by T cells from humans latently infected with <i>Mycobacterium tuberculosis</i> By comparing native HBHA with recombinant HBHA produced in <i>Mycobacterium smegmatis</i> (rHBHA-<i>Ms</i>), we could link antigenic differences to differences in the methylation profile. Peptide scan analyses led to the discovery of a peptide containing methyl lysines recognized by a mAb that binds to native HBHA ∼100-fold better than to rHBHA-<i>Ms</i> This peptide was also recognized by T cells from latently infected humans, as evidenced by IFN-γ release upon peptide stimulation. The nonmethylated peptide did not induce IFN-γ, arguing that the methyl lysines are part of the T cell epitope.