Construction and characterization of chimeric hepatitis C virus E2 glycoproteins: analysis of regions critical for glycoprotein aggregation and CD81 binding

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Abstract
We compared the ability of two closely related truncated E2 glycoproteins (E2660) derived from hepatitis C virus (HCV) genotype 1a strains Glasgow (Gla) and H77c to bind a panel of conformation-dependent monoclonal antibodies (MAbs) and CD81. In contrast to H77c, Gla E2660 formed disulfide-linked high molecular mass aggregates and failed to react with conformation-dependent MAbs and CD81. To delineate amino acid (aa) regions associated with protein aggregation and CD81 binding, several Gla–H77c E2660 chimeric glycoproteins were constructed. Chimeras C1, C2 and C6, carrying aa 525–660 of Gla E2660, produced disulfide-linked aggregates and failed to bind CD81 and conformation-dependent MAbs, suggesting that amino acids within this region are responsible for protein misfolding. The presence of Gla hypervariable region 1 (aa 384–406) on H77 E2660, chimera C4, had no effect on protein folding or CD81 binding. Chimeras C3 and C5, carrying aa 384–524 or 407–524 of Gla E2660, respectively, were recognized by conformation-dependent MAbs and yet failed to bind CD81, suggesting that amino acids in region 407–524 are important in modulating CD81 interaction without affecting antigen folding. Comparison of Gla and H77c E2660 aa sequences with those of genotype 1a and divergent genotypes identified a number of variant amino acids, including two putative N-linked glycosylation sites at positions 476 and 532. However, introduction of G476N–G478S and/or D532N in Gla E2660 had no effect on antigenicity or aggregation.