A sensitive cell-based assay for the detection of residual infectious West Nile virus.

Ensuring complete viral inactivation is critical for the safety of vaccines based on an inactivated virus. Detection of residual infectious virus is dependent on sensitivity of the assay, sample volume analyzed and the absence of interference with viral infection. Here we describe the development and qualification of a sensitive cell-based assay for the detection of residual infectious West Nile Virus (WNV). The results of the assay are in good agreement with the assumption that at low concentrations the number of infectious units in relatively small samples follows a Poisson distribution. The assay can detect 1 infectious unit with a confidence of 99%, provides statistical controls for interference and can easily be scaled up to test large amounts of vaccine material. Furthermore, we show equivalence in sensitivity between the cell-based assay and an in vivo assay for detection of infectious WNV. Finally, the assay has been used for successful release testing of clinical lots of inactivated WNV vaccine. Given the principle and generic setup of the method we envision broad applicability to the detection of very low concentrations of infectious virus.

Structural changes and molecular interactions of hydrophobin SC3 in solution and on a hydrophobic surface.

The hydrophobin SC3 belongs to a class of small proteins functioning in the growth and development of fungi. Its unique amphipathic property and remarkable surface activity make it interesting not only for biological studies but also for medical and industrial applications. Biophysical studies have revealed that SC3 possesses at least three distinct conformations, named "soluble-state SC3" for the protein in solution, and "alpha-helical-state SC3" and "beta-sheet-state SC3" for the different states of the protein associated at a hydrophobic-water interface. The present fluorescence study shows that the microenvironment of the dansyl-labeled N terminus of soluble-state SC3 is relatively hydrophobic, whereas it is hydrophilic for alpha-helical-state and beta-sheet-state SC3. Fluorescence collisional quenching indicates that the N terminus of soluble-state SC3 is more solvent-accessible than those of alpha-helical-state and beta-sheet-state SC3, with Stern-Volmer constants for acrylamide of 4.63, 0.02, and 0.2 M(-1) for the different states, respectively. Fluorescence resonance energy transfer measurements show that soluble-state SC3 tends to associate in solution but dissociates in TFA. Fluorescence energy transfer was eliminated by conversion of soluble-state SC3 to alpha-helical-state SC3 on a hydrophobic surface, indicating a spatial separation of the molecules in this state. By inducing the beta-sheet state, structural changes were observed, both by CD and by fluorescence, that could be fit to two exponentials with lifetimes of about 10 min and 4 h. Molecules in the beta-sheet state also underwent a slow change in spatial proximity on the hydrophobic surface, as revealed by the reappearance of fluorescence resonance energy transfer in time.

Hydrophobins, the fungal coat unravelled.

Hydrophobins are among the most surface active molecules and self-assemble at any hydrophilic-hydrophobic interface into an amphipathic film. These small secreted proteins of about 100 amino acids can be used to make hydrophilic surfaces hydrophobic and hydrophobic surfaces hydrophilic. Although differences in the biophysical properties of hydrophobins have not yet been related to differences in primary structure it has been established that the N-terminal part, at least partly, determines wettability of the hydrophilic side of the assemblage, while the eight conserved cysteine residues that form four disulphide bridges prevent self-assembly of the hydrophobin in the absence of a hydrophilic-hydrophobic interface. Three conformations of class I hydrophobins have been identified: the monomeric state, which is soluble in water, the alpha-helical state, which is the result of self-assembly at a hydrophobic solid, and the beta-sheet state, which is formed during self-assembly at the water-air interface. Experimental evidence strongly indicates that the alpha-helical state is an intermediate and that the beta-sheet state is the end form of assembly. The latter state has a typical ultrastructure of a mosaic of 10 nm wide rodlets, which have been shown to resemble the amyloid fibrils.

Structural and functional role of the disulfide bridges in the hydrophobin SC3.

Hydrophobins function in fungal development by self-assembly at hydrophobic-hydrophilic interfaces such as the interface between the fungal cell wall and the air or a hydrophobic solid. These proteins contain eight conserved cysteine residues that form four disulfide bonds. To study the effect of the disulfide bridges on the self-assembly, the disulfides of the SC3 hydrophobin were reduced with 1,4-dithiothreitol. The free thiols were then blocked with either iodoacetic acid (IAA) or iodoacetamide (IAM), introducing eight or zero negative charges, respectively. Circular dichroism and infrared spectroscopy showed that after opening of the disulfide bridges SC3 is initially unfolded. IAA-SC3 did not self-assemble at the air-water interface upon shaking an aqueous solution. Remarkably, after drying down IAA-SC3 or after exposing it to Teflon, it refolded into a structure similar to that observed for native SC3 at these interfaces. Iodoacetamide-SC3 on the other hand, which does not contain extra charges, spontaneously refolded in water in the amyloid-like beta-sheet conformation, characteristic for SC3 assembled at the water-air interface. From this we conclude that the disulfide bridges of SC3 are not directly involved in self-assembly but keep hydrophobin monomers soluble in the fungal cell or its aqueous environment, preventing premature self-assembly.

Structural characterization of the hydrophobin SC3, as a monomer and after self-assembly at hydrophobic/hydrophilic interfaces.

Hydrophobins are small fungal proteins that self-assemble at hydrophilic/hydrophobic interfaces into amphipathic membranes that, in the case of Class I hydrophobins, can be disassembled only by treatment with agents like pure trifluoroacetic acid. Here we characterize, by spectroscopic techniques, the structural changes that occur upon assembly at an air/water interface and upon assembly on a hydrophobic solid surface, and the influence of deglycosylation on these events. We determined that the hydrophobin SC3 from Schizophyllum commune contains 16-22 O-linked mannose residues, probably attached to the N-terminal part of the peptide chain. Scanning force microscopy revealed that SC3 adsorbs specifically to a hydrophobic surface and cannot be removed by heating at 100 degrees C in 2% sodium dodecyl sulfate. Attenuated total reflection Fourier transform infrared spectroscopy and circular dichroism spectroscopy revealed that the monomeric, water-soluble form of the protein is rich in beta-sheet structure and that the amount of beta-sheet is increased after self-assembly on a water-air interface. Alpha-helix is induced specifically upon assembly of the protein on a hydrophobic solid. We propose a model for the formation of rodlets, which may be induced by dehydration and a conformational change of the glycosylated part of the protein, resulting in the formation of an amphipathic alpha-helix that forms an anchor for binding to a substrate. The assembly in the beta-sheet form seems to be involved in lowering of the surface tension, a potential function of hydrophobins.

Inhibitory effects of neuroleptics on debrisoquine oxidation in man.

Liver oxidative metabolism, assessed by debrisoquine hydroxylation test, was studied in 107 healthy volunteers and in 71 patients with or without neuroleptic drug treatment. The mean metabolic ratio (MR = debrisoquine/4-hydroxydebrisoquine excretion in the urine) was 2.8 +/- 0.1 (s.e. mean) in the control group, six persons being poor metabolizers of debrisoquine (MR greater than or equal to 12.6). The mean MR (12.1 +/- 1.5) was significantly higher in those 42 patients taking neuroleptics than in patients without neuroleptics (0.8 +/- 0.1). In the former group, seventeen patients had a MR exceeding 12.6. Oral contraceptives, antiepileptics, benzodiazepines and progestin derivates did not increase MR values, the highest individual ratio being 2.72 in those subjects not receiving neuroleptics. These results suggest a probable competitive inhibition of oxidative metabolism by neuroleptics. This is a phenomenon of potential clinical importance both in patients with an inherited poor metabolic capacity and in patients receiving other drugs like beta-adrenoceptor blocking agents and tricyclic antidepressants oxidized by the same enzyme system.