Conformational aspects of HIV-1 integrase inhibition by a peptide derived from the enzyme central domain and by antibodies raised against this peptide

Monospecific antibodies were raised against a synthetic peptide K159 (SQGVV ESMNKELKKIIGQVRDQAEHLKTA) reproducing the segment 147-175 of HIV-1 integras e (IN). Synthesis of substituted and truncated analogs of K159 led us to id entify the functional epitope reacting with antibodies within the C-termina l portion 163-175 of K159. Conformational studies combining secondary struc ture predictions, CD and NMR spectroscopy together with ELISA assays, showe d that the greater is the propensity of the epitope for helix formation the higher is the recognition by anti-K159. Both the antibodies and the antige nic peptide K159 exhibited inhibitory activities against IN. In contrast, n either P159, a Pro-containing analog of K159 that presents a kink around pr oline but with intact epitope conformation, nor the truncated analogs encom passing the epitope, were inhibitors of LN. While the activity of antibodie s is restricted to recognition of the sole epitope portion, that of the ant igenic K159 likely requires interactions of the peptide with the whole 147- 175 segment in the protein [Sourgen F., Maroun, R.G., Frere, V., Bouziane, A., Auclair, C., Troalen, F. & Fermandjian, S. (1996) fur. J. Biochem. 240, 765-773]. Actually, of all tested peptides only K159 was found to fulfill conditions of minimal number of helical heptads to achieve the formation of a stable coiled-coil structure with the IN 147-175 segment. The binding of antibodies and of the antigenic peptide to this segment of IN hampers the binding of IN to its DNA substrates in filter-binding assays. This appears to be the main effect leading to inhibition of integration. Quantitative an alysis of filter-binding-assay curves indicates that two antibody molecules react with IN implying that the enzyme is dimeric within these experimenta l conditions. Together, present data provide an insight into the structure- function relationship for the 147-175 peptide domain of the enzyme. They al so strongly suggest that the functional enzyme is dimeric. Results could he lp to assess models for binding of peptide fragments to IN and to develop s tronger inhibitors. Moreover, K159 antibodies when expressed in viva might exhibit useful inhibitory properties.