Composition and molecular organization of lipids and proteins in the envelope of mycoplasmavirus MVL2

Abstract

MVL2 virus was purified from culture supernatants of infected Acholeplasma laidlawii cells by differential centrifugation, followed by velocity centrifugation in sucrose gradients. The purified virus contained 0.08 to 0.1 ,tmol of lipid phosphorous per ml of viral protein. Thin-layer chromatography of viral lipids revealed the presence of phospho-, glyco-, and phosphoglycolipids identical with those found in the host cell membrane, but the relative amount of phosphatidylglycerol was much lower than that in the virus. The fatty acid compositition of the viral lipids was, however, the same as that of the host membrane lipids. The lipids incorporated into the virus included lipids synthesized before and after infection. The freedom of motion of spin-labeled fatty acids in MVL2 depended markedly on temperature and on the position of the nitroxide group on the hydrocarbon chain of the probe, suggesting that the local environment of the probe has the properties of a lipid bilayer. Nevertheless, the lipid hydrocarbon chains in MVL2 appear to be less mobile than those in membranes of the host cells. Polyacrylamide gel electrophoresis of purified MVL2 revealed four major and about five minor polypeptide bands. None of the polypeptide bands gave a positive periodic acid-Schiff reaction. Lactoperoxidase-mediated iodination, followed by proteolytic digestion of intact MVL2 particles, revealed that at least two major polypeptides are localized on the external surface of the viral envelope. Acholeplasma laidlawii harbors three distinct virus groups, designated MVL1, MVL2, and MVL3 (10, 11, 16, 19, 20). MVL2 was found to be sensitive to detergents and organic solvents, whereas MVL1 and MVL3 were not (12, 19). Electron microscopy of sectioned MVL2 preparations showed the spherical virus particles to be bounded by a membrane-like structure (12). This observation, when combined with sensitivity to detergents, was taken to suggest that MVL2 is an enveloped, lipid-containing virus. The aim of the present study was to characterize the components of the MVL2 envelope and to compare its composition and molecular organization with those of the cell membrane of the host. 0.5 ml of an overnight culture of A. laidlawii and spread over 100-mm-diameter tryptose agar plates. The plates were allowed to dry and then placed in a 37°C incubator. Plaques were counted after 24 h of incubation. 717

Half a Century of Research on Membrane-Containing Bacteriophages: Bringing New Concepts to Modern Virology

“…Based on the location of the membrane, phages can be roughly divided into three subclasses: (i) viruses in which the membrane is located underneath an icosahedral protein capsid; (ii) viruses in which the membrane (envelope) is the outermost layer of the virion, surrounding an icosahedral protein capsid, and; (iii) viruses in which the genome is enclosed by a proteinaceous lipid vesicle with pleomorphic appearance without any rigid protein capsid (Table 1). The lipid composition of plasmaviruses largely follows the lipid composition of its host cell membrane [19]. However, in most cases the lipids are incorporated into the virion selectively.…”