Structural insights into the distinct protective mechanisms of human antibodies targeting ZIKV NS1

Antibodies targeting non-structural protein 1 (NS1) confer protection against Zika virus (ZIKV). Although monoclonal antibodies (MAbs) 3G2 and 4B8 are more potent than MAb 4F10 in suppressing ZIKV infection in neonatal mice models, the epitopes are unclear. Herein, we determined the Cryo-electron microscopy (Cryo-EM) structures of ZIKV NS1 in complex with five human antibodies at 2.6–2.9 Å resolution. Group I antibodies (3G2 and 4B8) recognize the previously unreported epitopes on the outer surface of the NS1 dimer. The unique binding mode of Group I antibodies led to a stronger recognition of the cell surface form of NS1 and completely inhibited secreted form non-structural protein 1 (sNS1)-induced endothelial permeability via their immunoglobulin G (IgG) and Fab. Group II antibodies (4F10, 2E11, and 14G5) recognize common epitopes in the distal end of the β-ladder domain, with a blockade efficiency that may be related to their affinity for the sNS1 protein and the presence of full-length IgG. These findings elucidate the correlation between epitope recognition and protective efficacy of anti-NS1 antibodies and highlight the diagnostic and therapeutic potential of 3G2 and 4B8.