Lipid and protein contributions to the membrane surface potential of vesicular stomatitis virus probed by a fluorescent pH indicator, 4-heptadecyl-7-hydroxycoumarin

Electrostatic and structural properties of complexes involving plasmid DNA and cationic lipids commonly used for gene delivery

The present study is aimed to characterize the interactions between plasmid DNA and cationic, large unilamellar vesicles, 110+/-20nm in size, composed of lipids commonly used for transfections including DOTAP/DOPE (mole ratio 1/1), DOTAP/DOPC (mole ratio 1/1), 100% DOTAP, or DC-CHOL/DOPE (mole ratio 1/1). [

ABBREVIATIONS

DOTAP, N-(1-(2,3-dioleoyloxy)propyl)-N,N,N-trimethylammonium chloride; DOPE, 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine; DOPC, 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine; DC-CHOL, 3 beta-[N-(N',N'-dimethylaminoethane)carbamoyl] cholesterol]. A novel approach of combining Gouy-Chapman calculations and fluorescence measurements of the pH at the surface of lipid assemblies by the fluorophore 4-heptadecyl-7-hydroxycoumarin showed that electrostatic parameters played a key role in the instantaneous formation of the DNA-lipid complexes upon addition of different amounts of plasmid DNA to cationic liposomes in 20 mM Hepes buffer (pH 7.4). Addition of large amounts of plasmid DNA leads to neutralization of 60% of the protonated DC-CHOL in DC-CHOL/DOPE (1/1) assemblies and 80% of the DOTAP in lipid assemblies. The characterization of these electrostatic parameters of the complexes suggests better and closer surrounding of plasmid DNA by lipids when DOPE is present. Time-dependent static light-scattering measurements monitored the formation of complexes and also showed that these complexes were highly unstable with respect to size at DNA/cationic lipid molar ratios between 0.2 and 0.8.

Comparison between hepatitis B surface antigen (HBsAg) particles derived from mammalian cells (CHO) and yeast cells (Hansenula polymorpha): composition, structure and immunogenicity

The composition, structure and immunogenicity of hepatitis B surface antigen (HBsAg) particles derived from Chinese hamster ovary (CHO) cells and from cells of the yeast Hansenula polymorpha were compared. The particles were similar in size distribution (mean 20-33 nm), in shape (spherical), in gross composition (protein to lipid weight ratio of 60:40), and in types of lipids (phospholipids > > sterols = sterol esters = triacylglycerols). Differences related to genetic engineering and type of host cells were found in peptide and lipid compositions. CHO-HBsAg has three peptides: S, M and L, each in two forms of glycosylation, while the Hansenula-HBsAg has only the nonglycosylated S peptide. The electrical surface potential at the lipid/water interface of HBsAg derived from Hansenula is more negative than that of HBsAg derived from CHO, which was close to neutrality. Although the numbers of cysteine residues (all in the S peptides) are identical (14), 11 of them are free thiols in the CHO-HBsAg, compared with three to four in the Hansenula-HBsAg. The fact that 85% of the phospholipids are hydrolyzed by phospholipase C and that all the aminophospholipids react with trinitrobenzenesulfate suggests that the particles derived from both cell types are either leaky vesicles or have a lipoprotein-like structure. Subcutaneous injection into mice of fluorescein-isothiocyanate-labeled HBsAg particles from both sources resulted in their accumulation in the marginal sinus of lymph nodes. The humoral responses to subcutaneous injection into mice of CHO- and Hansenula-HBsAg were similar: however, the cytotoxic T lymphocyte response to CHO-HBsAg was lower.

The influence of dextran sulfate on influenza A virus fusion with erythrocyte membranes

Dextran sulfate suppresses the low pH-induced fusion of influenza virus A/Brazil 11/78 with erythrocyte membranes, as shown by fluorescence dequenching assay, using the fluorophore octadecylrhodamine B chloride (R18). Inhibition of fusion was maximal at pH 5.0, while at higher pH values (> 5.6) fusion was not affected. Hemolysis of intact red blood cells by influenza A virus at low pH values is also prevented by dextran sulfate. The inhibiting effect of the polymer is mainly ascribed to repression of virus attachment. Evidence is given that the conformational change of the virus envelope protein hemagglutinin (HA) responsible for triggering fusion is not affected by the polymer.

Human acid beta-glucosidase: use of sphingosyl and N-alkyl-glucosylamine inhibitors to investigate the properties of the active site

Human acid beta-glucosidase (D-glucosyl-N-acylsphingosine glucohydrolase, EC 3.2.1.45) cleaves the beta-glucosidic bonds of glucosylceramide and synthetic beta-glucosides. The specificity of binding to the active site of this enzyme was evaluated using series of inhibitors including synthetic sphingosines, N-alkyl(Cn)-deoxynojirimycins (1,5-dideoxy-5-iminoglucose) and N-Cn-glucosylamines. The sphingosines were rapidly reversible inhibitors with maximal potency (IC50 approximately 78-150 micro M) at chain lengths of 14-18 carbons. The presence of unsaturation between C4 and C5 was required for inhibition of enzyme activity. Neither the nature of this bond (double or triple bond) nor the presence of erythro or threo configurations at C2 influenced inhibitory potency. The N-C10- to N-C14-deoxynojirimycins were rapidly reversible inhibitors with Ki approximately 8.5 nM. In comparison, the 1-amino glucose derivatives, i.e., N-Cn-glucosylamines (n = 12-18), were more potent (IC50 approximatley 0.3-3 nM) and their maximal inhibitory potencies were dependent on time as well as enzyme and substrate concentrations: i.e., the N-C12- to N-C18-glucosylamines were competitive, slow-tight binding inhibitors. Analyses of progress curves at various N-Cn-glucosylamine (n = 14-18) concentrations indicated the formation of rapidly dissociating initial EI collison complex which then undergoes a conformational change to a slowly reversible EI complex. These results were consistent with the long chain N-Cn-glucosylamines being reaction intermediate analogues and with this enzyme's hydrolytic mechanism requiring a conformational change during the transition state.

Exclusion of poly(ethylene glycol) from liposome surfaces

The electrophoretic mobility of vesicles is measured for concentrations of poly(ethylene glycol) from 0 wt.% to 10 wt.%. Mixtures of phosphatidylcholines and phosphatidic acid are used. The zeta potential calculated from the electrophoretic mobility and the viscosity of the suspension becomes more negative for all vesicles studied. Binding of poly(ethylene glycol) to the phospholipid surface by addition of the poly(oxyethylene)-containing surfactant C12E8 has the opposite effect and a decrease of the zeta potential is observed. Independent measurements of the surface potential of the vesicles in the presence of PEG by use of a positively charged spin probe and ESR spectroscopy and a fluorescent pH indicator and fluorescence spectroscopy show that actually the surface potential is not changed. A theory of the electrophoretic behaviour of vesicles in the presence of PEG is given which explains the contradiction between the two methods. It is assumed that the polymer is excluded from the vesicle surface (depletion layer) and that the viscosity near the surface is lower than the viscosity in the bulk phase. The thickness of the depletion layer is calculated from the experiments. The decrease of the zeta potential in the presence of poly(oxyethylene) chains linked to the vesicle surface results from the friction increase.