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Journal of Virology, October 2000, p. 9099-9105, Vol. 74, No. 19
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Low-Level Secretion of Human Hepatitis B Virus Virions Caused by Two Independent, Naturally Occurring Mutations (P5T and L60V) in the Capsid Protein

Sophie Le Pogam, Thomas Ta-Tung Yuan, Gautam Kumar Sahu, Soma Chatterjee, and Chiaho Shih*

Center for Tropical Diseases, Department of Pathology, University of Texas Medical Branch, Galveston, Texas 77555-0609

Received 4 May 2000/Accepted 14 July 2000

The functional significance of naturally occurring variants of human hepatitis B virus (HBV) remains largely unknown. Previously, we reported an immature secretion phenotype caused by a highly frequent mutation at amino acid 97 of the HBV core (capsid) protein (HBcAg). This phenotype is characterized by a nonselective and excessive secretion of virions containing an immature genome of single-stranded viral DNA. To extend our study of virion secretion to other naturally occurring variants, we have characterized mutations at HBcAg codons 5, 38, and 60 via site-directed mutagenesis. Although the phenotype of the mutation at codon 38 is nearly identical to that for the wild-type virus, our study reveals that a single mutation at codon 5 or 60 exhibits a new extracellular phenotype with significantly reduced virion secretion yet maintains normal intracellular viral DNA replication. A complementation study indicates that the mutant core protein alone is sufficient for the "low-secretion" phenotype. Furthermore, the low-secretion phenotype of the codon 5 mutant appears to be induced by the loss of a parental proline residue, rather than by the gain of a new amino acid. Our study underscores the core protein as another crucial determinant in virion secretion, in addition to the known envelope proteins. Our present results suggest that a very precise structure of both alpha -helical and nonhelical loop regions of the entire HBcAg molecule is important for virion secretion. The low-secretion variants may contribute to the phenomenon of gradually decreasing viremia in chronic carriers during the late phase of persistent infection.

* Corresponding author. Mailing address: Center for Tropical Diseases, Department of Pathology, University of Texas Medical Branch, Galveston, TX 77555-0609. Phone: (409) 772-2563. Fax: (409) 747-2429. E-mail: cshih{at}utmb.edu.

Journal of Virology, October 2000, p. 9099-9105, Vol. 74, No. 19
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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