Alteration of hepatitis A virus (HAV) particles by a soluble form of HAV cellular receptor 1 containing the immunoglobin-and mucin-like regions

Hepatitis A virus (HAV) infects African green monkey kidney cells via HAV cellular receptor 1 (havcr-1). The ectodomain of havcr-1 contains an N-terminal cysteine-rich immunoglobin-like region (D1), followed by a mucin-like region that extends D1 well above the cell surface. D1 is required for binding of HAV, and a soluble construct containing D1 fused to the hinge and Fc portions of human immunoglobin G1 (IgG1), D1-Fc, bound and neutralized HAV inefficiently. However, D1-Fc did not alter the virions. To determine whether additional regions of havcr-1 are required to trigger uncoating of HAV, we constructed D1muc-Fc containing D1 and two-thirds of the mucin-like region fused to the Fc and hinge portions of human IgG1. D1muc-Fc neutralized 10 times more HAV than did D1-Fc. Sedimentation analysis in sucrose gradients showed that treatment of HAV with 20 to 200 nM D1muc-Fc disrupted the majority of the virions, whereas treatment with 2 nM D1muc-Fc had no effect on the sedimentation of the particles. Treatment of HAV with 100 nM D1muc-Fc resulted in low-level accumulation of 100- to 125S particles. Negative-stain electron microscopy analysis revealed that the 100- to 125S particles had the characteristics of disrupted virions, such as internal staining and diffuse edges. Quantitative PCR analysis showed that the 100- to 125S particles contained viral RNA. These results indicate that D1 and the mucin-like region of havcr-1 are required to induce conformational changes leading to HAV uncoating.