Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 115, Issue 18, Pages 4773-4778Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1721345115
Keywords
hepatitis E virus; antibody neutralization; immunological decoy; leaky translation; quasi-envelopment
Categories
Funding
- National Natural Science Foundation of China [81701576]
- Natural Science Foundation of Fujian Province, China [2016105201]
- Principal Funds from Xiamen University
- Pinnacle Research Award in Liver Diseases from the American Association for the Study of Liver Diseases Foundation
- National Institute of Allergy and Infectious Diseases [AI122228, AI137912]
- Nationwide Children's Hospital
- NIH [S10 OD018056]
- NATIONAL INSTITUTE OF ALLERGY AND INFECTIOUS DISEASES [R21AI137912, R21AI122228, R01AI126890] Funding Source: NIH RePORTER
- OFFICE OF THE DIRECTOR, NATIONAL INSTITUTES OF HEALTH [S10OD018056] Funding Source: NIH RePORTER
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The enterically transmitted hepatitis E virus (HEV) adopts a unique strategy to exit cells by cloaking its capsid (encoded by the viral ORF2 gene) and circulating in the blood as quasi-enveloped particles. However, recent evidence suggests that the majority of the ORF2 protein present in the patient serum and supernatants of HEV-infected cell culture exists in a free form and is not associated with virus particles. The origin and biological functions of this secreted form of ORF2 (ORF2(S)) are unknown. Here we show that production of ORF2(S) results from translation initiated at the previously presumed AUG start codon for the capsid protein, whereas translation of the actual capsid protein (ORF2(C)) is initiated at a previously unrecognized internal AUG codon (15 codons downstream of the first AUG). The addition of 15 amino acids to the N terminus of the capsid protein creates a signal sequence that drives ORF2(S) secretion via the secretory pathway. Unlike ORF2(C), ORF2(S) is glycosylated and exists as a dimer. Nonetheless, ORF2(S) exhibits substantial antigenic overlap with the capsid, but the epitopes predicted to bind the putative cell receptor are lost. Consistent with this, ORF2(S) does not block HEV cell entry but inhibits antibody-mediated neutralization. These results reveal a previously unrecognized aspect in HEV biology and shed new light on the immune evasion mechanisms and pathogenesis of this virus.
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