title: An alkyl imidate labeling study of the organization of phospholipids and proteins in the lipid-containing bacteriophage PR4.
abstract: The structure of the lipid-containing bacteriophage PR4 was studied using two alkyl imidates, ethyl acetimidate (EAI), a reagent permeant to lipid bilayers and isethionyl acetimidate (IAI), which is impermeant to membranes. The virion is an icosahedral particle consisting of a protein coat surrounding a membrane of phospholipid and protein which in turn encloses the DNA genome. Upon exposure to the permeant reagent, EAI, 50% of the phosphatidylethanolamine (PE) molecules reacted rapidly (half-life less than 10 min). A similar fraction of the PE also reacted with IAI, the impermeant reagent. The remaining half of the PE molecules reacted slowly with EAI (half-life of 80 min) and failed to react with IAI. All of the phage proteins reacted with both EAI and IAI (except a DNA-associated protein which reacted only with EAI). These labeling results indicate that the phage membrane consists of a lipid bilayer and that at least a portion of each phage protein (except the DNA-associated protein) is exposed on the external face of the lipid bilayer. Several of the membrane proteins could be cross-linked either to the phage membrane PE after EAI treatment or to phage phosphatidylglycerol after periodate treatment. The major structural protein of the phage was readily cross-linked to PG but failed to cross-link to PE suggesting that the protein specifically interacts with PG.
mesh_terms: D003432:Cross-Linking Reagents; D007096:Imidoesters; D007202:Indicators and Reagents; D007513:Isethionic Acid / Q000031:analogs & derivatives; D007700:Kinetics; D008051:Lipid Bilayers; D010743:Phospholipids / Q000032:analysis*; D012483:Salmonella Phages / Q000648:ultrastructure*; D012486:Salmonella typhimurium / Q000648:ultrastructure*; D014764:Viral Proteins / Q000032:analysis*
chemical_list: D003432:Cross-Linking Reagents; D007096:Imidoesters; D007202:Indicators and Reagents; D008051:Lipid Bilayers; D010743:Phospholipids; D014764:Viral Proteins; C014539:ethyl acetimidate; C020761:isethionyl acetimidate; D007513:Isethionic Acid