Selection and Partial Characterization of Dengue 2 Virus Mutants That Induce Fusion at Elevated pH

Abstract

Two types of dengue (DEN) 2 virus mutants were selected either by repeated exposure to acidic pH (acid mutant, AM), or by the addition of ammonium chloride to Aedes albopictus C6/36 cells prior to and during viral infection (fusion mutant, FM). Both mutants grew more slowly than the parent strain and induced smaller plaques in Vero cells. The 50% fusion from within index for both mutants occurred at least 0.65 pH units higher than with the wild-type DEN virus. A single amino acid substitution (Asn-153 to Asp) was found in the envelope (E)-glycoprotein of the AM virus. Three amino acid substitutions were detected on the E-glycoprotein of the FM virus: IIe-6 to Met, Ash-134 to Ser, and Ash-153 to Tyr. No mutations were found in the precursor to the membrane protein, prM. The DEN virus E-glycoprotein has two potential glycosylation sites: Asn-67 and Asn- 153. The loss of the potential glycosylation site at Asn-153 or the change in the chemical characteristics resultant from the amino acid substitutions in both mutants implicates these regions of the E-glycoprotein in virus-mediated membrane fusion.