Identification of a variant B-specific neutralizing epitope on glycoprotein H of human herpesvirus-6

This study identified a variant B-specific neutralizing epitope on human herpesvirus-6 (HHV-6) glycoprotein H (gH) recognized by monoclonal antibody OHV3. Researchers expressed gH from HHV-6A (strain U1102) and HHV-6B (strain HST) using a T7-vaccinia virus transient expression system. OHV3 specifically reacted with HST gH but not U1102 gH in immunoprecipitation and immunofluorescence assays. Using chimeric gH constructs and site-directed mutagenesis, the epitope region was mapped to amino acids 272-422 of HST gH. Sequence analysis revealed seven amino acid differences between the two strains in this region. Testing individual mutations showed that arginine at position 389 of HST gH is the critical determinant of OHV3 recognition. When arginine was substituted with lysine, OHV3 failed to react with the protein. Conversely, introducing arginine at position 389 in U1102 gH (which normally has lysine) allowed OHV3 binding. The epitope appears to be conformational, as the N-terminus region is also required for proper structure.

Key findings

• Arginine at position 389 of HHV-6B glycoprotein H is the critical amino acid determinant recognized by neutralizing monoclonal antibody OHV3
• The neutralizing epitope is variant-specific, with OHV3 reacting only to HHV-6B gH and not HHV-6A gH
• The epitope is conformational, involving amino acids 272-422 with contributions from regions extending to amino acid 526
• OHV3 neutralizes infectivity in a complement-independent manner, making it a potential therapeutic target
• The variant-specific neutralizing epitope correlates with amino acid differences between HHV-6A and HHV-6B strains that may relate to their distinct biological properties