title: The cowpox virus fusion regulator proteins SPI-3 and hemagglutinin interact in infected and uninfected cells.
abstract: The serpin SPI-3 and the hemagglutinin (HA) encoded by cowpox virus (CPV) block cell-cell fusion, and colocalize at the cell surface. wtCPV does not fuse cells, but inactivation of either gene leads to fusion. SPI-3 mAb added to wtCPV-infected cells caused fusion, confirming that SPI-3 protein at the cell surface prevents fusion. The SPI-3 mAb epitope mapped to an 85-amino acid region at the C-terminus. Removal of either 44 residues from the SPI-3 C-terminus or 48 residues following the N-terminal signal sequence resulted in fusion. Interaction between SPI-3 and HA proteins in infected cells was shown by coimmunoprecipitation. SPI-3/HA was not associated with the A27L "fusion" protein. SPI-3 and HA were able to associate in uninfected cells in the absence of other viral proteins. The HA-binding domain in SPI-3 resided in the C-terminal 229 residues, and did not include helix D, which mediates cofactor interaction in many other serpins.
authors.affiliation: Department of Molecular Genetics and Microbiology, Box 100266/1600 SW Archer Road, ARB R2-231, University of Florida, Gainesville, FL 32610-0266, USA. pturner@mgm.ufl.edu
authors.forename: Peter C
authors.initials: PC
authors.lastname: Turner
authors.forename: Richard W
authors.initials: RW
authors.lastname: Moyer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D000914:Antibodies, Viral; D002460:Cell Line; D002462:Cell Membrane / Q000821:virology; D002522:Chlorocebus aethiops; D015608:Cowpox virus / Q000235:genetics / Q000276:immunology / Q000472:pathogenicity* / Q000502:physiology*; D018604:Epitope Mapping; D006389:Hemagglutinins, Viral / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D008561:Membrane Fusion / Q000235:genetics / Q000502:physiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015843:Serpins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D014162:Transfection; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000502:physiology*
chemical_list: D000911:Antibodies, Monoclonal; D000914:Antibodies, Viral; D006389:Hemagglutinins, Viral; D011994:Recombinant Proteins; D015843:Serpins; D014764:Viral Proteins