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Bichko V, Barik S, Taylor J
Phosphorylation of the hepatitis delta virus antigens
Journal of Virology (1997) 71:512-518.
We used two-dimensional electrophoresis (nonequilibrium pH gradient electrophoresis followed by sodium dodecyl sulfate-10% polyacrylamide gel electrophoresis) coupled with P-32 labeling and immunoblotting detection with I-125-protein A to detect and quantitate phosphorylation of the large and small forms of the delta antigen (delta Ag-L and delta Ag-S, respectively). Analysis of delta Ag species from the serum and liver of an infected woodchuck as well as delta Ag species expressed in and secreted from transfected Huh7 cells revealed the following. (i) No detectable phosphorylation of delta Ag-S occurred, (ii) In virions from the serum of an infected animal and in the particles secreted from cotransfected cells, none of the delta Ag-L was phosphorylated. (iii) Only in the infected liver and in transfected cells was any phosphorylation detected; it corresponded to a monophosphorylated form of delta Ag-L. Given these results, we carried out serine-to-alanine mutagenesis of the delta Ag-L to determine whether the monophosphorylation was predominantly at a specific site on the unique 19-amino-acid (aa) extension, We mutated each of the two serines, aa 207 and 210, on this extension and also the serine at aa 177. These three mutations had no significant effect on phosphorylation. In contrast, mutagenesis to alanine of the cysteine at aa 211, which normally acts as the acceptor for farnesylation, completely inhibited phosphorylation, Our interpretation is that the site(s) of phosphorylation is probably not in the 19- aa extension unique to delta Ag-L and that phosphorylation of delta Ag-L may depend upon prior farnesylation. The possible significance of the intracellular phosphorylated forms of delta Ag-L is discussed.
Publication Date: 1997-01-01.
Last updated on Wednesday, March 04, 2020