CONFORMATIONAL-CHANGES BETWEEN HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 NUCLEOCAPSID PROTEIN NCP7 AND ITS PRECURSOR NCP15 AS DETECTED BY ANTI-NCP7 MONOCLONAL-ANTIBODIES

The nucleocapsid protein NCp15 of human immunodeficiency virus type 1 (HIV-1) is a small basic protein with two zinc fingers. It is required for virion morphogenesis and synthesis of proviral DNA. As the first step in our study of the structural domains involved in the various fu nctions of this protein, 18 monoclonal antibodies (MAbs) were isolated . The epitopes of NCp7 recognized by the MAbs were mapped using synthe tic peptides representing overlapping sequences and truncated forms of NCp7. These anti-NCp7 MAbs were investigated by ELISA and real-time b iospecific interaction analysis (BIAcore). Five classes of anti-NCp7 M Abs were characterized. Three classes (14 MAbs) were directed against continuous epitopes, one in the N-terminal part, another next to the s econd zinc finger and the third in the C-terminal part of the protein. Two other classes comprised four MAbs reacting only with the entire N Cp7 and not with any of the small overlapping peptides used, suggestin g that these MAbs were directed against conformational epitopes. The a nti-NCp7 MAbs directed against linear epitopes were able to react effi ciently with both NCp7 and NCp15, the NCp7 precursor: whereas the anti -NCp7 MAbs directed against conformational epitopes did not react with NCp15. Interestingly, most of the anti-NCp7 MAbs directed against con formational epitopes were capable of inhibiting the tight interaction between NCp7 and the HIV-1 replication primer tRNA(Lys,3). In contrast , most of the MAbs directed against linear epitopes did not inhibit th is interaction.