Fine Characterization of the Antigenic Site Within the Flap Region in the Protease Protein of HIV-1

The aspartate protease encoded by human immunodeficiency virus type 1 is essential for cleavage of the gag and gag-pol precursor proteins. The majority of HIV-1-antibody-positive sera react with the protease. In this study we used a substitution set of peptides for detailed characterization of the earlier defined antigenic site (aa 44-58) within the central "flap" region, also important in the context of conformational flexibility during protease inhibitor binding. We found that isoleucine at position 54 was important for creating an antigenic site required for binding of anti-HIV-1 sera. The identification of structurally essential amino acids in the flap region of HIV-1 PR may have important implications in future development of antiviral drugs.