Phospholipids of lipid-containing bacteriophages and their transbilayer distribution

In this study we used electro-spray ionization mass-spectrometry to determine phospholipid class and molecular species compositions in bacteriophages PM2, PRD1, Bam35 and phi6 as well as their hosts. To obtain compositional data of the individual leaflets, phospholipid transbilayer distribution in the viral membranes was studied. We found that 1) the membranes of all studied bacteriophage are enriched in PG as compared to the host membranes, 2) molecular species compositions in the phage and host membranes are similar, and 3) phospholipids in the viral membranes are distributed asymmetrically with phosphatidylglycerol enriched in the outer leaflet and phosphatidylethanolamine in the inner one (except Bam35). Alternative models for selective incorporation of phospholipids to phages and for the origins of the asymmetric phospholipid transbilayer distribution are discussed. Notably, the present data are also useful when constructing high resolution structural models of bacteriophages, since diffraction methods cannot provide a detailed structure of the membrane due to high motility of the lipids and lack of symmetric organization of membrane proteins.

Lipid-containing bacterial viruses (bacteriophages) are useful models in which to study membrane assembly and lipid-protein interactions. Interpretation of high-resolution structures of these viruses require knowledge on the detailed compositions of their components. In this study we determined phospholipid class and molecular species compositions in bacteriophages PM2, PRD1, Bam35 and phi6 as well as their hosts. Quantitative electro-spray ionization mass-spectrometry was used to obtain this compositional data. In addition, the phospholipid transbilayer distribution in the viral membranes was studied in order to determine the phospholipid compositions of individual sides of these membranes. We found that 1) there is relatively more of phosphatidylglycerol in bacteriophage membranes as compared to the host membranes, but the molecular species compositions in the viral and host membranes are similar, and 2) phospholipids in the viral membranes are distributed asymmetrically with phosphatidylglycerol enriched in the outer side of the mmebrane and phosphatidylethanolamine in the inner one (except in one virus).