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Influenza B virus BM2 protein is transported through the trans-Golgi network as an integral membrane protein
Shinji Watanabe1, Masaki Imai, Yoshiro Ohara
1Laboratory of Influenza Viruses, Department of Virology 3, National Institute of Infectious Diseases, Tokyo 208-0011, Japan.
Abstract:
A bicistronic mRNA transcribed from the influenza B virus RNA segment 7 encodes two viral proteins, matrix protein M1 and uncharacterized small protein BM2. In the present study, we focused on the cytoplasmic transport and cellular membrane association of BM2. Immunofluorescence studies of virus-infected cells indicated that BM2 accumulated at the Golgi apparatus immediately after synthesis and then was transported to the plasma membrane through the trans-Golgi network. Localization of a set of BM2 deletion mutants revealed that the N-terminal half of BM2 (residues 2 to 50) was crucial for its transport; in particular, the deletion of residues 2 to 23, deduced to be a transmembrane domain, resulted in diffused distribution of the protein throughout the entire cell. Sucrose gradient flotation and biochemical analyses of the membrane showed that BM2 was tightly associated with cellular membranes as an integral membrane protein. Oligomerization of BM2 was demonstrated by coprecipitation of differentially epitope-tagged BM2 proteins. Taken together, these results strongly suggest that BM2 is integrated into the plasma membrane at the N-terminal hydrophobic domain as fourth membrane protein, in addition to hemagglutinin, neuraminidase, and NB, of the influenza B virus.
Insights
Influenza B virus protein BM2 travels from the Golgi to the plasma membrane. BM2 integrates into the cell membrane as an integral protein, crucial for viral function.
Area of Science:
- Virology
- Cell Biology
- Molecular Biology
Background:
- Influenza B virus RNA segment 7 encodes matrix protein M1 and the small protein BM2.
- The function and cellular localization of BM2 have remained largely uncharacterized.
Purpose of the Study:
- To investigate the cytoplasmic transport and cellular membrane association of the influenza B virus protein BM2.
- To determine the structural domains of BM2 responsible for its localization and membrane integration.
Main Methods:
- Immunofluorescence microscopy of virus-infected cells and BM2 deletion mutants.
- Sucrose gradient flotation and biochemical membrane association analyses.
- Coprecipitation assays to assess BM2 oligomerization.
Main Results:
- BM2 accumulates at the Golgi apparatus and is transported to the plasma membrane via the trans-Golgi network.
- The N-terminal half of BM2 (residues 2-50), including a predicted transmembrane domain (residues 2-23), is essential for its proper transport and localization.
- BM2 is an integral membrane protein tightly associated with cellular membranes and capable of oligomerization.
Conclusions:
- BM2 is integrated into the plasma membrane through its N-terminal hydrophobic domain.
- BM2 functions as a fourth membrane protein of the influenza B virus, alongside hemagglutinin, neuraminidase, and NB.
- Understanding BM2's membrane integration and transport provides insights into influenza B virus assembly and pathogenesis.