Defining of MAbs-neutralizing sites on the surface glycoproteins Gn and Gc of a hantavirus using vesicular stomatitis virus pseudotypes and site-directed mutagenesis

ABSTRACT Earlier four Monoclonal antibodies (MAbs) against surface glycoproteins Gn and Gc of Puumala virus (PUUV, genus Orthohantavirus , family Hantaviridae , order Bunyavirales ) were generated and for three MAbs with neutralizing capacity the localization of binding epitopes was predicted using pepscan and phage-display techniques. In this work, we produced vesicular stomatitis virus (VSV) particles pseudotyped with the Gn and Gc glycoproteins of PUUV and applied site-directed mutagenesis to dissect the structure of neutralizing epitopes. Replacement of cysteine amino acid (aa) residues with alanines resulted in pseudotype particles with diminished (16 to 18%) neut-titers; double Cys→Ala mutants, as well as mutants with bulky aromatic and charged residues replaced with alanines, have shown even stronger reduction in neut-titers (from 25% to the escape phenotype). In silico modelling of the neut-epitopes supported the hypothesis that these critical residues are located on the surface of viral glycoprotein molecules and thus can be recognized by the antibodies indeed. Similar pattern was observed in experiments with mutant pseudotypes and sera collected from patients suggesting that these neut-epitopes are utilized in a course of human PUUV infection. IMPORTANCE Neutralization of viruses by antibodies is one of the key events in infection. We identified a set of mutations in the surface proteins of PUUV that reduced the virus-neutralizing activity of MAbs. Moreover, we found three mutants with escaped phenotype. These data will help understanding the mechanisms of hantavirus neutralization and assist construction of vaccine candidates.