Antigenic switching of hepatitis B virus by alternative dimerization of the capsid protein

MA DiMattia, NR Watts, SJ Stahl, JM Grimes… - Structure, 2013 - cell.com
MA DiMattia, NR Watts, SJ Stahl, JM Grimes, AC Steven, DI Stuart, PT Wingfield
Structure, 2013cell.com
Chronic hepatitis B virus (HBV) infection afflicts millions worldwide with cirrhosis and liver
cancer. HBV e-antigen (HBeAg), a clinical marker for disease severity, is a nonparticulate
variant of the protein (core antigen, HBcAg) that forms the building-blocks of capsids. HBeAg
is not required for virion production, but is implicated in establishing immune tolerance and
chronic infection. Here, we report the crystal structure of HBeAg, which clarifies how the
short N-terminal propeptide of HBeAg induces a radically altered mode of dimerization …
Summary
Chronic hepatitis B virus (HBV) infection afflicts millions worldwide with cirrhosis and liver cancer. HBV e-antigen (HBeAg), a clinical marker for disease severity, is a nonparticulate variant of the protein (core antigen, HBcAg) that forms the building-blocks of capsids. HBeAg is not required for virion production, but is implicated in establishing immune tolerance and chronic infection. Here, we report the crystal structure of HBeAg, which clarifies how the short N-terminal propeptide of HBeAg induces a radically altered mode of dimerization relative to HBcAg (∼140° rotation), locked into place through formation of intramolecular disulfide bridges. This structural switch precludes capsid assembly and engenders a distinct antigenic repertoire, explaining why the two antigens are cross-reactive at the T cell level (through sequence identity) but not at the B cell level (through conformation). The structure offers insight into how HBeAg may establish immune tolerance for HBcAg while evading its robust immunogenicity.
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