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Novel acylation of poxvirus A-type inclusion proteins
K H Martin1, C A Franke, D E Hruby
1Department of Microbiology, Center for Gene Research and Biotechnology, Oregon State University, Corvallis 97331-3804, USA.
Abstract:
Myristylation is one of several post-translational modifications that occur on vaccinia virus (VV) proteins. Previously, time course labeling of VV-infected cells with myristic acid had indicated that five late proteins (17, 25, 36, 38 and 92 kDa) are myristylated. Four of these proteins were mapped to the E7R, L1R, AI6L and G9R open-reading frames, respectively, because of the predicted presence of the N-myristyltransferase recognition sequence (M-G-X-X-X-S/T/A) at their amino termini. In contrast, computer analyses of large (80-100 kDa) VV open reading frames did not reveal any predicted species with this N-terminal motif. By immunoprecipitation with monospecific sera and transient expression of cloned gene products, the myristylated 92-kDa protein has been demonstrated to be the A-type inclusion protein encoded by the Western Reserve (WR) strain of VV. Labeling of cowpox virus (CPV) infected cells with myristic acid indicated that the 160-kDa A-type inclusion protein appears to be myristylated as well. Both the VV 92-kDa and the CPV 160-kDa A-type inclusion proteins labeled with myristic acid were stable to hydroxylamine treatment, suggesting an amide linkage between the fatty acid and the acceptor protein. HPLC analysis confirmed that the 92-kDa protein was in fact myristylated. This data suggests that poxvirus ATI proteins may be subject to a novel type of internal myristylation modification, and the roles such modifications may play in the replication cycles of these viruses is discussed.
Insights
This study reveals that vaccinia virus (VV) A-type inclusion (ATI) proteins undergo myristylation, a post-translational modification. This modification appears to involve an internal fatty acid linkage, suggesting a novel mechanism in poxvirus replication.
Area of Science:
- Virology
- Molecular Biology
- Post-Translational Modifications
Background:
- Myristylation is a common post-translational modification of viral proteins.
- Previous studies identified five myristylated late vaccinia virus (VV) proteins, with four linked to N-terminal myristyltransferase recognition sequences.
- Large VV proteins lacked predicted N-terminal myristylation motifs.
Purpose of the Study:
- To identify the myristylated 92-kDa protein in VV-infected cells.
- To investigate the nature of myristylation in poxvirus A-type inclusion (ATI) proteins.
- To explore potential novel myristylation mechanisms in poxviruses.
Main Methods:
- Myristic acid labeling of VV and cowpox virus (CPV)-infected cells.
- Immunoprecipitation with monospecific sera.
- Transient expression of cloned gene products.
- Hydroxylamine stability assays.
- High-Performance Liquid Chromatography (HPLC) analysis.
Main Results:
- The 92-kDa myristylated protein in VV was identified as the A-type inclusion (ATI) protein.
- The 160-kDa ATI protein from CPV also appeared to be myristylated.
- Myristylation of both VV and CPV ATI proteins was stable to hydroxylamine, indicating an amide linkage.
- HPLC confirmed myristylation of the 92-kDa VV protein.
Conclusions:
- Poxvirus ATI proteins are subject to myristylation.
- This modification likely involves an internal amide linkage, suggesting a novel myristylation pathway.
- Further research is needed to understand the functional significance of ATI protein myristylation in poxvirus replication.