Characterization of a glycoprotein fusogen isolated from Sendai virus

Conformation and stability of Sendai virus fusion protein

The conformation and stability of Sendai virus fusion (F) protein were studied by circular dichroism spectroscopy, and the protein predictive models of Chou and Fasman and Robson and Suzuki were used to elucidate the secondary structure of Sendai virus F protein. The F protein conformation is predicted to contain 33% alpha-helix, 53% beta-sheet and 15% beta-turn by the Chou and Fasman model, and 30% alpha-helix, 55% beta-sheet, 9% beta-turn and 7% random coil by the Robson and Suzuki model. C.d. studies of F protein purified in the presence of the non-ionic detergent, n-octylglucoside, indicated the presence of 49% alpha-helix and 31% beta-sheet at pH 7.0, 54% alpha-helix and 28% beta-sheet at pH 9.0 and 50% alpha-helix and 23% beta-sheet at pH 5.4. A small change in conformation of the protein occurred when the pH was titrated from 7.0 to 5.4 and from 7.0 to 9.0 and a more pronounced conformational change occurred when the pH was changed from 9.0 to 5.4. The F protein in 0.2% n-octylglucoside was resistant to denaturation by 4 M guanidine hydrochloride, the reducing agent 20 mM mercaptoethanol, and to increases in temperature from 5 to 80 degrees C. Monoclonal anti-F protein antibody showed an increased binding to whole virus when the pH was changed from 7.0 to 9.0. The antibody binding was decreased when the pH was shifted from 9.0 to 5.4 Maximum haemolytic activity was observed with virus that was preincubated at pH 8.0.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of DNA-intercalating dye to monitor cell fusion and microinjection

A conventional method for microinjection, using erythrocyte ghosts as the injection vector, has been modified to provide a protocol for the highly efficient delivery of small quantities of material into the cytoplasm of target cells. The technique is applicable for use with a variety of proteins, sugars, nucleotides and dyes. When the intercalating dye propidium iodide is included within the sealed ghosts their subsequent fusion with target cells can be continuously monitored by fluorescence spectroscopy, providing a convenient and sensitive parameter of cell-cell fusion. The protocol can be adapted for use with both adherent and non-adherent target cells, and can be used to monitor the relative effectiveness of a variety of fusogenic agents.

Preparation and characterization of F-protein vesicles isolated from Sendai virus by means of octyl glucoside

We have demonstrated that Triton X-100 is always present in F-protein vesicles at concentrations that can provoke cell lysis. In order to avoid any misinterpretation of the fusogenic capacity of this protein, we solubilized the Sendai virus using octyl glucoside, which can be totally removed from the F protein preparation in less than 16 h by dialysis in the presence of absorbent beads. F-glycoprotein preparations preserved their ability to lyse erythrocytes in the presence of lectins and to induce cell-vesicle fusion as demonstrated by ESR studies. These vesicles were characterized by electron microscopy and SDS-polyacrylamide gel electrophoresis. Lipid analysis of these preparations by thin-layer chromatography indicated that they had the same proportion of lipids as virus envelopes, with slight variations in the sphingomyelin content and the cholesterol/phospholipid molar ratio. F-protein vesicles of different sizes can be obtained by adding exogenous lipids before detergent removal. The hemolytic activity of the vesicles was retained over a large range of lipid concentrations. We conclude that F-protein vesicles prepared with octyl glucoside are convenient tools for studying the fusogenic mechanism of this protein and improving the fusion process between liposomes and cells.

The activity of membranes reconstituted from HVJ envelope proteins and lipids to induce hemolysis and fusion between liposomes and erythrocytes

A simple method for preparation of lipid-free envelope proteins (HN protein and F protein) of HVJ (Sendai virus) was developed. Reconstituted 'envelopes' were then prepared from envelope proteins and various lipids by the detergent dialysis method, and the activity to induce hemolysis and fusion between liposome and erythrocyte was studied. Lipid-free envelope protein aggregates could induce hemolysis and liposome-erythrocyte fusion. The activity was however greatly augmented by incorporation of envelope proteins into membrane of viral total lipids. Hemolytic and fusogenic activity was somewhat augmented by incorporation of envelope proteins into dipalmitoylphosphatidylcholine/cholesterol (1:1, molar ratio) and dimyristoylphosphatidylcholine/cholesterol (1:1), though the augmentation was lower than that observed with viral total lipids. When 'envelopes' were reconstituted with the proteins and viral total lipids supplemented with phosphatidylethanolamine, two kinds of 'envelopes' were prepared; one was permeable to Dextran (Mr 75000) and hemolytic, and the other was impermeable to Dextran and nonhemolytic. The latter acquired hemolytic activity after subjection to freezing and thawing, and its barrier function was lost concomitantly. The study suggests that envelope proteins (HN protein and F protein) could function without lipids but their activity was greatly influenced by not only the composition of additional lipids but also mode of arrangement of components on the reconstituted membranes.