Mouse monoclonal antibodies directed against the HTLV-I protease recognize epitopes internal to the dimer.

The proteases (PR) of retroviruses are expressed as gag-PR fused polyprotein. The active PR is a dimer obtained after the aggregation of the gag and gag-pro precursors, which leads to the formation and the release of the viral particle. Subsequently, in the cell, the PR is present essentially as a monomeric polyprotein. To mimic the antigenic properties of such an intracellular form of the PR, we produced a monomeric form of the HTLV-I (human T-cell leukemia virus, type-I) PR fused to the maltose binding protein (MBP-PR). Monoclonal antibodies (mabs) directed against MBP-PR were developed. Three mabs were obtained that recognized different epitopes. Two were directed against the NH2-terminus, a region that contributes to the dimerization interface. The other was specific to a peptide that lines the substrate binding pocket. This latter epitope is located just downstream of the D-T-G peptide of the catalytic site. The two identified regions contained the amino acids Asp6, Arg10 and Asp36, which were previously shown to be important in the stabilization of the dimer. In view of the localization of the recognized epitopes, these mabs will be useful for inhibition studies of the HTLV-I PR by intracellular immunization.