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The interferon-induced Mx protein of chickens lacks antiviral activity
D Bernasconi1, U Schultz, P Staeheli
1Institut für Mikrobiologie und Hygiene, Abteilung Virologie, University of Freiburg, Germany.
Abstract:
cDNA sequencing revealed that chick Mx protein consists of 705 amino acids. Its 84 N-terminal amino acids show no significant sequence homology to other Mx proteins. They are followed by 514 residues that include a tripartite GTP binding consensus motif. This region shows 50-70% sequence identity to mammalian and duck Mx proteins. Sequences near the C terminus, including a leucine zipper motif, are also conserved, whereas the intervening 19 amino acids lack sequence similarity. This unique sequence corresponds to a highly variable region in mammalian Mx proteins, suggesting that it serves as a spacer between functional domains. Chick and mouse cells transiently transfected with cDNA expression constructs synthesized chick Mx protein at a level that could easily be detected with specific antibodies. Chick Mx protein in such cells was mainly cytoplasmic and had a granular appearance. Permanently transfected cell lines expressing high levels of chick Mx protein could not be established, suggesting low metabolic stability of chick Mx protein or incompatibility with cell proliferation. The antiviral activity of chick Mx protein was tested at the single-cell level using immunofluorescence techniques. Transfected cells expressing chick Mx protein showed no enhanced resistance to influenza A virus, vesicular stomatitis virus, Thogoto virus, or Sendai virus. Thus, chick Mx joins the list of Mx proteins without recognized antiviral activity, supporting the concept that Mx proteins serve unrelated functions.
Insights
Chick Mx protein, a key antiviral factor, was analyzed. Despite conserved domains, chick Mx protein lacks antiviral activity against common viruses, suggesting diverse Mx protein functions.
Area of Science:
- Molecular Biology
- Virology
- Immunology
Background:
- Mx proteins are interferon-induced proteins known for their antiviral properties.
- The chick Mx protein's structure and function have not been fully elucidated.
Purpose of the Study:
- To characterize the chick Mx protein, including its sequence, expression, localization, and antiviral activity.
Main Methods:
- cDNA sequencing was used to determine the full-length sequence of chick Mx protein.
- Transient transfection of chick and mouse cells was performed to express chick Mx protein.
- Immunofluorescence techniques and various viruses (influenza A, vesicular stomatitis virus, Thogoto virus, Sendai virus) were used to assess antiviral activity.
Main Results:
- Chick Mx protein consists of 705 amino acids with conserved GTP-binding and leucine zipper motifs, but a unique N-terminal region and intervening sequence.
- Chick Mx protein was expressed in transfected cells, localized to the cytoplasm, and showed granular appearance.
- No enhanced resistance to tested viruses was observed in cells expressing chick Mx protein.
Conclusions:
- Chick Mx protein possesses structural similarities to functional Mx proteins but lacks antiviral activity.
- This finding supports the hypothesis that Mx proteins may have evolved to serve diverse, non-antiviral functions in different species.