The HIV-1 Integrase [alpha]4-Helix Involved in LTR-DNA Recognition Is also a Highly Antigenic Peptide Element

• Published in: PloS one 2010-12, Vol.5 (12)
• Main Authors: Azzi, Sandy, Parissi, Vincent, Maroun, Richard G, Eid, Pierre, Mauffret, Olivier, Fermandjian, Serge
• Format: Article
• Language: English
• Subjects: Analysis; Antigenic determinants; DNA; Enzyme-linked immunosorbent assay; Enzymes; HIV; Monoclonal antibodies; Peptides
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0016001

Monoclonal antibodies (MAbas) constitute remarkable tools to analyze the relationship between the structure and the function of a protein. By immunizing a mouse with a 29mer peptide (K159) formed by residues 147 to 175 of the HIV-1 integrase (IN), we obtained a monoclonal antibody (MAba4) recognizing an epitope lying in the N-terminal portion of K159 (residues 147-166 of IN). The boundaries of the epitope were determined in ELISA assays using peptide truncation and amino acid substitutions. The epitope in K159 or as a free peptide (pep-a4) was mostly a random coil in solution, while in the CCD (catalytic core domain) crystal, the homologous segment displayed an amphipathic helix structure ([alpha]4-helix) at the protein surface. Despite this conformational difference, a strong antigenic crossreactivity was observed between pep-a4 and the protein segment, as well as K156, a stabilized analogue of pep-a4 constrained into helix by seven helicogenic mutations, most of them involving hydrophobic residues. We concluded that the epitope is freely accessible to the antibody inside the protein and that its recognition by the antibody is not influenced by the conformation of its backbone and the chemistry of amino acids submitted to helicogenic mutations. In contrast, the AA [right arrow]Glu mutations of the hydrophilic residues Gln148, Lys156 and Lys159, known for their interactions with LTRs (long terminal repeats) and inhibitors (5