Topology and immunoreactivity of capsid proteins in hepatitis A virus

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 with 125I and a solid-phase oxidant. The order of labelling intensity in complete particles was VP1 much greater than VP3 greater than VP2; labelling of VP4 was undetectable. When the particles were denatured with sodium dodecyl sulfate at 100 degrees C before iodination, the labelling efficiency was 6 times higher and the order of labelling intensity was VP3 greater than VP2 greater than 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 33000, 29000 and 28000 daltons.