Topology and immunoreactivity of capsid proteins in hepatitis A virus

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Abstract
Hepatitis A virus (HAV) was propagated in a hepatoma cell line and complete viral particles with a density of 1.34 g/ml were purified from cell extracts. The topography of the viral proteins (VPs) was studied by surface labelling with125I and a solid-phase oxidant. The order of labelling intensity in complete particles was VP1≫VP3>VP2; labelling of VP4 was undetectable. When the particles were denatured with sodium dodecyl sulfate at 100°C before iodination, the labelling efficiency was 6 times higher and the order of labelling intensity was VP3>VP2>VP1. After denaturation, the viral proteins no longer reacted with human anti-HAV antibody. The results suggest that (i) as with other picornaviruses, HAV exposes an essential part of VP1 at its surface whereas VP3 and especially VP2 are more hidden; (ii) naturally immunized individuals do not form detectable amounts of antibodies against the denatured capsid proteins. The apparent molecular weights of the VPs were 33 000, 29 000 and 28 000 daltons.