Characterization of two engineered dimeric Zika virus envelope proteins as immunogens for neutralizing antibody selection and vaccine design.

The envelope protein of Zika virus (ZIKV) exists as a dimer on the mature viral surface and is an attractive antiviral target because it mediates viral entry. However, recombinant soluble wild-type ZIKV envelope (wtZE) might preferentially exist as monomer (monZE). Recently, it has been shown that the A264C substitution could promote formation of dimeric ZIKV envelope protein (ZEA264C), requiring further characterization of purified ZEA264C for its potential applications in vaccine development. We also noted that ZEA264C, connected by disulfide bond, might be different from the noncovalent native envelope dimer on the virion surface. Because the antibody Fc fragment exists as dimer and is widely used for fusion protein construction, here we fused wtZE to human immunoglobulin G1 (IgG1) Fc fragment (ZE-Fc) for noncovalent wtZE dimerization. Using a multistep purification procedure, we separated dimeric ZEA264C and ZE-Fc, revealing that they both exhibit typical β-sheet-rich secondary structures and stabilities similar to those of monZE. The binding activities of monZE, ZEA264C, and ZE-Fc to neutralizing antibodies targeting different epitopes indicated that ZEA264C and ZE-Fc could better mimic the native dimeric status, especially in terms of the formation of tertiary and quaternary epitopes. Both ZEA264C and ZE-Fc recognize a ZIKV-sensitive cell line as does monZE, indicating that the two constructs are still functional. Furthermore, a murine immunization assay disclose that ZEA264C and ZE-Fc elicit more neutralizing antibody responses than monZE does. These results suggest that the two immunogen candidates ZEA264C and ZE-Fc have potential utility for neutralizing antibody selection and vaccine design against ZIKV.