Qianru Wang1, Yanli Qin2, Jing Zhang1, Lucy Jia3, Shuwen Fu1, Yongxiang Wang1, Jisu Li3, Shuping Tong4. 1. Department of Pathobiology, Key Laboratory of Medical Molecular Virology, School of Basic Medical Sciences, Fudan University, Shanghai, China. 2. Department of Infectious Diseases, Huashan Hospital, Fudan University, Shanghai, China. 3. Liver Research Center, Rhode Island Hospital and Warren Alpert Medical School of Brown University, Providence, RI, USA. 4. Department of Pathobiology, Key Laboratory of Medical Molecular Virology, School of Basic Medical Sciences, Fudan University, Shanghai, China; Liver Research Center, Rhode Island Hospital and Warren Alpert Medical School of Brown University, Providence, RI, USA. Electronic address: shuping_tong_md@brown.edu.
Abstract
Hepatitis B virus (HBV) is the prototype of hepadnaviruses, which can be subgrouped into orthohepadnaviruses infecting mammals, avihehepadnaviruses of birds, metahepadnaviruses of fish, and herpetohepadnaviruses of amphibians and reptiles. The middle (M) envelope protein and e antigen are new additions in the evolution of hepadnaviruses. They are alternative translation products of the transcripts for small (S) envelope and core proteins, respectively. For HBV, e antigen is converted from precore/core protein by removal of N-terminal signal peptide followed by furin-mediated cleavage of the basic C-terminus. This study compared old and newly discovered hepadnaviruses for their envelope protein and e antigen expression or processing. The S protein of bat hepatitis B virus (BHBV) and two metahepadnaviruses is probably myristoylated, in addition to two avihepadnaviruses. While most orthohepadnaviruses express a functional M protein with N-linked glycosylation near the amino-terminus, most metahepadnaviruses and herpetohepadnaviruses probably do not. These viruses and one orthohepadnavirus, the shrew hepatitis B virus, lack an open precore region required for e antigen expression. Potential furin cleavage sites (RXXR sequence) can be found in e antigen precursors of orthohepadnaviruses and avihepadnaviruses. Despite much larger precore/core proteins of avihepadnaviruses and their limited sequence homology with those of orthohepadnaviruses, their proximal RXXR motif can be aligned with a distal RXXR motif for orthohepadnaviruses. Thus, furin or another basic endopeptidase is probably the shared enzyme for hepadnaviral e antigen maturation. A precore-derived cysteine residue is involved in forming intramolecular disulfide bond of HBV e antigen to prevent particle formation, and such a cysteine residue is conserved for both orthohepadnaviruses and avihepadnaviruses. All orthohepadnaviruses have an X gene, while all avihepadnaviruses can express the e antigen. M protein expression appears to be the most recent event in the evolution of hepadnaviruses.
n class="Species">Hepatitis B virus (pan> class="Species">HBV) is the prototype of hepadnaviruses, which can be subgrouped into orthohepadnaviruses infecting mammals, avihehepadnaviruses of birds, metahepadnaviruses of fish, and herpetohepadnaviruses of amphibians and reptiles. The middle (M) envelope protein and e antigen are new additions in the evolution of hepadnaviruses. They are alternative translation products of the transcripts for small (S) envelope and core proteins, respectively. For HBV, e antigen is converted from precore/core protein by removal of N-terminal signal peptide followed by furin-mediated cleavage of the basic C-terminus. This study compared old and newly discovered hepadnaviruses for their envelope protein and e antigen expression or processing. The S protein of bat hepatitis B virus (BHBV) and two metahepadnaviruses is probably myristoylated, in addition to two avihepadnaviruses. While most orthohepadnaviruses express a functional M protein with N-linked glycosylation near the amino-terminus, most metahepadnaviruses and herpetohepadnaviruses probably do not. These viruses and one orthohepadnavirus, the shrew hepatitis B virus, lack an open precore region required for e antigen expression. Potential furin cleavage sites (RXXR sequence) can be found in e antigen precursors of orthohepadnaviruses and avihepadnaviruses. Despite much larger precore/core proteins of avihepadnaviruses and their limited sequence homology with those of orthohepadnaviruses, their proximal RXXR motif can be aligned with a distal RXXR motif for orthohepadnaviruses. Thus, furin or another basic endopeptidase is probably the shared enzyme for hepadnaviral e antigen maturation. A precore-derived cysteine residue is involved in forming intramolecular disulfide bond of HBV e antigen to prevent particle formation, and such a cysteine residue is conserved for both orthohepadnaviruses and avihepadnaviruses. All orthohepadnaviruses have an X gene, while all avihepadnaviruses can express the e antigen. M protein expression appears to be the most recent event in the evolution of hepadnaviruses.
Authors: Xupeng Hong; Laurie Luckenbaugh; David Perlman; Peter A Revill; Stefan F Wieland; Stephan Menne; Jianming Hu Journal: Hepatology Date: 2021-07 Impact factor: 17.298