Journal of General Virology, Vol 79, 2743-2751, Copyright © 1998 by Society for General Microbiology

ARTICLES

Normal phosphorylation of duck hepatitis B virus L protein is dispensable for infectivity

EV Grgacic, B Lin, EV Gazina, MJ Snooks and DA Anderson
Hepatitis Research Unit, Macfarlane Burnet Centre for Medical Research, Fairfield, Australia.

A fraction of the large surface protein (L) of duck hepatitis B virus (DHBV) is phosphorylated at serine or threonine residues (E. Grgacic & D. Anderson, Journal of Virology 68, 7344-7350, 1994). We now report the identification of phosphorylation sites in DHBV L protein. Using site-directed mutagenesis, we have identified serine-118 (S118) as the major phosphorylation site, accepting approximately 64% of the total phosphate groups incorporated in L, and resulting in retarded migration of phosphorylated L in SDS-PAGE. Proline-119 is indispensable for S118 phosphorylation. Mutation of other serine/threonine residues which are followed by prolines (T79, T89, S117 and T155) together with S118 further reduced phosphorylation to around 19% of wild-type. Non- equilibrium pH gel electrophoresis (NEPHGE) and SDS-PAGE of 33P- labelled L protein revealed two phosphorylated L species, while protein with the S118 to alanine mutation was detected as only one labelled species, consistent with multiple phosphorylations in wild-type L. Together, these results demonstrate that serine 118 is the major phosphorylation site for a proline-directed kinase, and that a proportion of L molecules are additionally phosphorylated at one of a number of secondary sites. DHBV mutants encoding L proteins with minimal phosphorylation (alanine mutants) or mimicking constitutive phosphorylation (aspartic acid mutants) remained infectious both in cell culture and in ducks, demonstrating that L phosphorylation may play only a minor role in DHBV replication.

This article has been cited by other articles:

				J. Chojnacki, D. A. Anderson, and E. V. L. Grgacic A Hydrophobic Domain in the Large Envelope Protein Is Essential for Fusion of Duck Hepatitis B Virus at the Late Endosome J. Virol., December 1, 2005; 79(23): 14945 - 14955. [Abstract] [Full Text] [PDF]

				E. V. L. Grgacic and D. A. Anderson St, a Truncated Envelope Protein Derived from the S Protein of Duck Hepatitis B Virus, Acts as a Chaperone for the Folding of the Large Envelope Protein J. Virol., May 1, 2005; 79(9): 5346 - 5352. [Abstract] [Full Text] [PDF]

				H. Guo, W. S. Mason, C. E. Aldrich, J. R. Saputelli, D. S. Miller, A. R. Jilbert, and J. E. Newbold Identification and Characterization of Avihepadnaviruses Isolated from Exotic Anseriformes Maintained in Captivity J. Virol., March 1, 2005; 79(5): 2729 - 2742. [Abstract] [Full Text] [PDF]

				E. V. L. Grgacic Identification of structural determinants of the first transmembrane domain of the small envelope protein of duck hepatitis B virus essential for particle morphogenesis J. Gen. Virol., June 1, 2002; 83(7): 1635 - 1644. [Abstract] [Full Text] [PDF]

				J.-J. Mu, H.-L. Wu, B.-L. Chiang, R.-P. Chang, D.-S. Chen, and P.-J. Chen Characterization of the Phosphorylated Forms and the Phosphorylated Residues of Hepatitis Delta Virus Delta Antigens J. Virol., December 1, 1999; 73(12): 10540 - 10545. [Abstract] [Full Text]

				K. Rothmann, M. Schnolzer, G. Radziwill, E. Hildt, K. Moelling, and H. Schaller Host Cell-Virus Cross Talk: Phosphorylation of a Hepatitis B Virus Envelope Protein Mediates Intracellular Signaling J. Virol., December 1, 1998; 72(12): 10138 - 10147. [Abstract] [Full Text] [PDF]