Mapping to completeness and transplantation of a group-specific, discontinuous, neutralizing epitope in the envelope protein of dengue virus.
Résumé
Dengue is caused by a taxonomic group of four viruses, dengue virus types 1-4 (DENV1-DENV4). A molecular understanding of the antibody-mediated protection against this disease is critical to design safe vaccines and therapeutics. Here, the energetic epitope of antibody mAb4E11, which neutralizes the four serotypes of DENV but no other flavivirus, and binds domain 3 (ED3) of their envelope glycoprotein, was characterized. Alanine-scanning mutagenesis of the ED3 domain from serotype DENV1 was performed and the affinities between the mutant domains and the Fab fragment of mAb4E11 were measured. The epitope residues (307-312, 387, 389 and 391) were at the edges of two distinct beta-sheets. Four residues constituted hot spots of binding energy. They were aliphatic and contributed to form a hydrophobic pocket (Leu308, Leu389), or were positively charged (Lys307, Lys310). They may bind the diversity residues of mAb4E11, H-Trp96-Glu97. Remarkably, cyclic residues occupy and block the hydrophobic pocket in all unrelated flaviviruses. Transplanting the epitope from the ED3 domain of DENV into those of other flaviviruses restored affinity. The epitope straddles residues of ED3 that are involved in virulence, e.g. Asn/Asp390. These results define the epitope of mAb4E11 as an antigenic signature of the DENV group and suggest mechanisms for its neutralization potency.