| Abstract: | ![]()
Abstract: The human monoclonal antibody, mAb 2F5, has broad HIV‐1 neutralizing activity and binds a conserved linear epitope within the envelope glycoprotein gp41 having a core recognition sequence ELDKWA. In this study, the structural requirements of this epitope for high‐affinity binding to mAb 2F5 were explored using peptide synthesis and competitive enzyme‐linked immunosorbant assay (ELISA). Expansion of the minimal epitope to an end‐capped, linear nonapeptide, Ac‐LELDKWASL‐amide, was sufficient to attain maximal affinity within the set of native gp41‐sequence peptides assayed. Scanning single‐residue alanine and d ‐residue substitutions then confirmed the essential recognition requirements of 2F5 for the central DKW sequence, and also established the importance of the terminal leucine residues in determining high‐affinity binding of the linear nonapeptide. Further studies of side‐chain and backbone‐modified analogs revealed a high degree of structural specificity for the DK sequence in particular, and delineated the steric requirements of the Leu3 and Trp6 residues. The nine‐residue 2F5 epitope, flanked by pairs of serine residues, retained a high affinity for 2F5 when it was conformationally constrained as a 15‐residue, disulfide‐bridged loop. However, analogs with smaller or larger loop sizes resulted in lower 2F5 affinities. The conformational effects of the gp41 C‐peptide helix immediately adjacent to the N‐terminal end of the ELDKWA epitope were examined through the synthesis of helix‐initiated analogs. Circular dichroism (CD) studies indicated that the α‐helical conformation was propagated efficiently into the LELDKWASL epitope, but without any significant effect on its affinity for 2F5. This study should guide the design of a second generation of conformationally constrained ELDKWA analogs that might elicit an immune response that mimics the HIV‐neutralizing actions of 2F5. |
