IDENTIFICATION OF CLASS-I MHC REGIONS WHICH BIND TO THE ADENOVIRUS E3-19K PROTEIN

The adenovirus early region 3 glycoprotein E3-19k binds to and inhibit s expression of class I major histocompatibility complex (MHC)-encoded molecules, which may help infected cells evade immune recognition. Th e role of specific regions of the class I MHC molecule in the interact ion with E3-19k was evaluated using a series of HLA-A2.1-, HLA-A2 vari ant-, and HLA-B7-expressing cell lines. The monoclonal antibody (mAb) W6/32, which recognizes a monomorphic epitope on class I MHC molecules , readily co-immunoprecipitated E3-19k with HLA-A2.1 and 14 different HLA-A2 variant molecules that differ from HLA-A2.1 by single amino aci d substitutions. Thus, no single residue tested in the regions of the class I MHC molecule that bind peptide or the T-cell receptor controls the binding to E3-19k. Additional immunoprecipitations performed with mAbs directed against well-defined epitopes on the surface of HLA-A2. 1 revealed a dichotomy in the ability of the mAbs to co-immunoprecipit ate HLA-A2.1 and E3-19k. The mAbs LGIII-220 (directed against the C-te rminal end of the alpha 1-helix), CR11-351 (directed against the N-ter minal end of the alpha 2-helix), and PA2.1 (directed against the middl e of the alpha 2-helix and an underlying beta-loop) readily co-precipi tated HLA-A2.1 and E3-19k. In contrast, mAbs MA2.1 (directed against t he N-terminal end of the alpha 1-helix and the C-terminal end of the a lpha 2-helix) and HO-2 (directed against the N-terminal end of the alp ha 1-helix) did not co-precipitate E3-19k with HLA-A2.1. Similarly, mA b MB40.2 (directed against residues 169-182 of HLA-B7) also did not co -precipitate E3-19k with HLA-B7. These studies lead to the conclusion that the N-terminal end of the alpha 1-helix and the C-terminal end of the alpha 2-helix play an important role in dictating the ability of the E3-19k protein to bind to the class I MHC molecule.