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Two forms of poliovirus VPg result from amino acid modification of a single viral protein
Abstract:
The protein (VPg) covalently attached to the 5' terminus of poliovirus RNA has been reported to resolve into two forms, separable by electrofocusing, yet the viral gene sequence predicts only one apparent gene for VPg. The two VPg species were separated and analyzed for structural differences. The protein contains no phosphorylated amino acid residues other than the junction tyrosine linked to the nucleic acid moiety. After isolation, the acidic form of VPg remains stable, but the more basic form again generates a distribution of both species. This suggests some lability or modification of at least one amino acid residue postsynthesis. The position of the alteration in the protein was localized to the amino-terminal tryptic peptide, containing nine amino acids.
Insights
Poliovirus protein VPg exists in two forms, despite a single gene. Structural analysis revealed post-synthesis modification in the amino-terminal peptide of the basic VPg form.
Area of Science:
- Virology
- Molecular Biology
- Protein Chemistry
Background:
- Poliovirus protein VPg, attached to viral RNA, presents as two forms.
- The viral gene sequence suggests only one VPg gene exists.
Purpose of the Study:
- To investigate the structural differences between the two VPg species.
- To identify the nature and location of post-synthesis modifications in poliovirus VPg.
Main Methods:
- Separation of VPg species by electrofocusing.
- Structural analysis of isolated VPg forms.
- Tryptic peptide mapping to localize modifications.
Main Results:
- Two VPg species were separated and analyzed.
- No phosphorylated amino acids were found except for the junction tyrosine.
- The basic VPg form showed instability, reverting to a mixture of both species.
- The modification was localized to the N-terminal tryptic peptide.
Conclusions:
- Poliovirus VPg undergoes post-synthesis modification.
- This modification affects at least one amino acid residue in the N-terminal peptide.
- The basic VPg form is likely a labile intermediate.