Herbert A. Blough

The lipids of paramyxoviruses: a comparative study of Sendai and Newcastle disease viruses.

Abstract The lipids of two paramyxoviruses, NDV-B1 and Sendai virus (propagated in ovo ), were analyzed by thin-layer and gas-liquid chromatography. Both viruses had relatively large amounts of phosphatidylethanolamine and phosphatidylserine and relatively small amounts of sphingomyelin and lecithin. Analysis of fatty acid methyl esters revealed that Sendai virus had 50% more unsaturated acids than did NDV, whereas long-chain saturates accounted for 40% of the total fatty acids of the NDV envelope. Glycolipids were detected in both viruses; in the case of NDV, these were hydrolyzed and the sugars characterized by gas-liquid chromatography. Galactose, mannose, and glucose were present in molar ratios of 7:1:1, and the glycolipids were tentatively identified as ceramide hexosides. It is suggested that changes in polar groups and acyl chains of viruses propagated in homolog membranes are determined by structural proteins of the viral envelope. Differences in fatty acyl chain composition and to a lesser extent, polar groupings, may account for the pleomorphism and other biological properties of lipid-containing viruses.

Effect of 2-deoxy-D-glucose on cell fusion induced by Newcastle disease and herpes simplex viruses.

Fusion from within induced by either Newcastle disease or Herpes simplex viruses is completely inhibited by treatment of infected cells with 10 mM 2-deoxy- D -glucose. Hemadsorption to cells infected with Newcastle disease virus is also prevented, and the dose response of inhibition is similar to that for fusion from within. In the case of Newcastle disease virus, fusion from within is prevented by addition of 2-deoxy- D -glucose at any time up to 4 hr after infection; thereafter, fusion becomes rapidly insensitive to addition of the analogue. Fusion from without by high concentrations of Newcastle disease virus particles is, on the other hand, not inhibited by 2-deoxy- D -glucose. These results suggest that inhibition of fusion from within is due to the failure of infected cells to synthesize essential glycoprotein(s) in the presence of the analogue.

Lipids in Viruses

Publisher Summary This chapter discusses lipids in viruses. Lipid forms an integral part of many viruses and exists either in the form of a continuous envelope or in lipoprotein complexes that surround a nucleoprotein core or helix. In general, the envelope can be described as a molecular container for the genetic material of the virus. Viruses are obligate intracellular parasites and are not known to carry genetic coding for enzymes involved in lipid synthesis. Hence, they generally contain the same classes of lipid as are found in the host cell or their membrane of assembly. Lipids make up 20–35% by weight of most viruses; however, there are exceptions such as vaccinia virus, which has only 5% lipid despite having a complex multimembrane envelope structure. Naked herpesvirus capsids closely resemble non-lipid-containing viruses such as adenovirus or polyoma virus, which are also assembled in the nucleus but show full infectivity without any envelope. Both naked and enveloped herpesvirus particles are found in infected cells; however, only enveloped particles are found in extracellular fluids.

The lipids of incomplete influenza virus

Abstract Standard influenza virus (A0/PR8/34) and incomplete virus of the von Magnus type were analyzed and compared. Virus propagated under conditions of serial undiluted passage had a lower molar ratio of cholesterol-phospholipid (0.6) than did standard virus. A comparison of phospholipids revealed decreased amounts of sphingomyelin and phosphatidylcholine together with increased amounts of phosphatidylethanolamine. Fatty acid profiles of the polar lipid fractions revealed a shift toward short-chain acids and long-chain polyunsaturated fatty acids. Neutral lipids, separated by a unidimensional, two-solvent system, revealed that incomplete virus had an increased amount of glycerides with a shift toward mono- and diglycerides. Such changes would tend to alter the packing of the lipids of influenza virus and lead to a more expanded and fluid envelope—accounting for the pleomorphism and defects in the envelope of the von Magnus type virus.

Myxovirus Envelope Proteins: A Directing Influence on the Faffy Acids of Membrane Lipids

Acyl chain compositions of the lipids of three strains of influenza virus show differences not anticipated from current theories of myxovirus assembly. Fatty acids of viruses with antigenically related envelope proteins show greater resemblance than those of an unrelated strain, which suggests that these proteins influence the composition of membrane lipids at the site of viral release.

Synthesis and turnover of lipids in monolayer cultures of BHK-21 cells

Abstract Synthesis and turnover of lipids in monolayer cultures of BHK-21 cells were investigated using three separate techniques: (a) relative rates of synthesis and turnover during short pulses; (b) rates at which the label was lost following equilibrium incorporation of label; (c) time required to reach equilibrium using different precursor molecules. With short pulses (1 h) of [2-3H]glycerol followed by a chase period of 22 h the half-life of major phospholipids was found to be 2 1 2 –4 h. These findings were confirmed by sequential labeling, i.e., equilibrium labeling cells with [2-14C]glycerol followed by a short pulse with [2-3H]glycerol and chases for 21 h. Evidence of rapid turnover was also found using [1,2-14C]choline. Diglycerides and triglycerides also showed evidence of rapid turnover. Under the conditions of these experiments, phosphatidylserine and phosphatidylinositol did not equilibrate and the reason for this is unknown. Based on these studies, lipids can be divided into three classes: those showing rapid turnover, e.g., phosphatidylcholine, di-, and triglycerides; those showing intermediate turnover, phosphatidylethanolamine; those showing a slow turnover (greater than 15 h), sphingomyelin and phosphatidylserine. Short pulse-chase studies with [2-3H]glycerol provides a good method for measuring relative rates of synthesis and turnover of phosphoglycerides and neutral glycerides in eukaryotic cells.

The effect of vitamin A on myxoviruses: II. Alterations in the lipids of influenza virus

Abstract The lipids of highly purified influenza virus (PR8), derived from cells treated with vitamin A, were analyzed and compared with PR8 obtained from normal allantoic cells. Total lipids were slightly lower in the vitamin A-treated virus, and this deficiency was primarily in the neutral lipid fraction. In comparison to PR8 controls, virus grown in the presence of vitamin A had two- to threefold increases in phosphatidylserine and phosphatidylinositol with concomitant decreases in sphingomyelin and phosphatidylethanolamine. Fatty acid profiles revealed increased amounts of palmitic acid (C 16:0 ) in the vitamin A-virus. Some differences were noted in certain minor fatty acids. Possible mechanisms for some of these changes are discussed. It is suggested that the rearrangement of acidic phospholipids within the viral envelope may produce leaflet-micellar transitions; such changes may account for the formation of filamentous myxoviruses as well as other aberrant forms. These observations provide additional evidence that the lipids of the host cell play an important role in determining the phenotype of enveloped viruses.

Glycosylation inhibitors block the expression of LAV/HTLV-III (HIV) glycoproteins

The glycosylation inhibitors 2-deoxy-D-glucose (2-dGlc) and, to a lesser extent, beta-hydroxynorvaline blocked the formation of syncytia in HIV (LAV/HTLV-III)-infected cells. Using monospecific polyclonal antibodies against recombinant envelope proteins gp110 and gp41 or monoclonal antibodies against env gp110, we could demonstrate a marked reduction in the immunoreactivity of these antigens in HIV-infected cells exposed to the glycosylation inhibitors. There was concomitant accumulation of core proteins p15 and p24, as shown by a solid phase radio-immunoassay, and a decreased oligosaccharide synthesis of env proteins, as monitored by the incorporation of [6-3H]GlcNAc. The reverse transcriptase was not affected by the compounds. Glycosylation inhibitors may be considered for the chemotherapy of AIDS or AIDS-related complex, or chemoprophylaxis of HIV-positive individuals.

Rapid turnover of principal phospholipids in BHK-21 cells

When BHK-21 cells are pulse-labeled with (2-3H)-glycerol for 1 hr, followed by chase periods of 0–22 hrs, rapid turnover of the newly synthesized major phospholipids is observed 2–6 hrs after termination of the pulse, indicating a half-life of 2.0–2.5 hrs. These lipids are also labeled to equilibrium rapidly, within 8 hrs, indicating that the bulk of these lipids participates in this rapid turnover.

The effect of herpesvirus infection and 2-deoxy-d-glucose on glycosphingolipids in BHK-21 cells

Abstract The effect of Herpes simplex virus (HSV) infection and 2-deoxy- d -glucose (dGlc) on the content of radiolabeled glycosphingolipids was studied in BHK-21 cells, after a 16 hr pulse with D-[3-3H]serine and [1-14C]palmitate. HSV infection caused a stimulated incorporation of the labeled precursors into total glycosphingolipids. The content of newly synthesized hematosides was reduced by 50% and newly synthesized ceramides, ceramide monohexosides, and ceramide dihexosides was increased two-to-threefold, suggesting a simplification of the glycolipid pattern. Treatment of infected and uninfected cells with 10 mM dGLc decreased radioactivity in all glycosphingolipids, whereas the ratio of cerarnide to its glycosylated derivatives increased. Glycosylation of endogenous ceramide was studied in vitro using microsomal fractions and UDP-[3H]glucose as the sugar donor. UDP-glucose:ceramide-glucosyltransferase activity was higher in microsomal fractions from HSV-infected cells than in preparations from controls, and treated cells had higher activities than untreated controls. Infection and dGlc treatment increased the number or accessibility of glucose acceptor sites. Thus, dGlc inhibits glycolipid synthesis in control and HSV-infected cells by blocking glycosylation of ceramide; the inhibition of glycolipid synthesis may have a role in virion assembly.