Inhibition Of Uncoating Research Articles

Serum albumin inhibits echovirus 7 uncoating.

Echoviruses induce a wide spectrum of diseases in man, the most severe being meningitis. In neonates, however, a severe systemic infection can be observed, leading to death. Serum albumin is the most abundant protein in plasma and most interstitial fluids, and its functions include osmoregulation and transport and delivery of hydrophobic molecules such as fatty acids and steroids. The results of cold-synchronized one-step growth analysis of echovirus 7 infection and sucrose-gradient analysis of A-particles suggest that physiological concentrations of albumin block echovirus 7 infection by inhibiting uncoating. The blockage was reversible and was still effective when albumin was added 30 min after virus adsorption. Inhibition of uncoating was confirmed by using rhodanine, a known specific inhibitor of echovirus uncoating. After removal of the albumin blockage, addition of rhodanine perpetuated the inhibition. Serum and interstitial albumin concentrations may limit echovirus infection in vivo and thereby act as an extracellular determinant for echovirus tropism.

Docking of a human rhinovirus neutralizing antibody onto the viral capsid.

The structure of the complex between the Fab fragment of a human rhinovirus serotype 2 (HRV2) neutralizing antibody (8F5) and a cross-reactive synthetic peptide derived from the viral capsid protein VP2 has been recently determined by crystallographic methods. The conformation adopted by the peptide was very similar to and could be superimposed onto the corresponding region of the viral protein VP2 of human rhinovirus 1A (HRV1A) whose three-dimensional structure is known. The structure of the Fab fragment determined in the complex was docked onto the viral capsid using the superimposition transformation found for the peptide. In the resulting model the Fab protrudes almost radially to about 60 A from the surface of the virion without any major steric problem. The Fab fragment was then placed on each one of the 60 equivalent epitopes using the T = 1 icosahedral symmetry of the virus. The closest pairs of Fab fragments are related by viral 2-fold axes and run almost parallel to each other without clashing. These axes of symmetry from the viral particle could thus be coincident with the dyad axes of the antibodies. Furthermore, comparison of the three-dimensional structure of the Fab/peptide complex with the structure of the Fab fragment alone indicates that the flexibility of the antibody's elbow would facilitate bivalent attachment to the same viral particle. In accordance with the docking results, experimental determination of the stoichiometry of binding yielded a ratio of 30 IgG molecules per virion also suggesting bivalent attachment of antibody 8F5 onto the viral particle. The neutralization of viral infectivity, being neither aggregation (this paper) nor inhibition of receptor binding, might be mainly achieved by reducing viral spread from cell to cell and/or inhibition of uncoating.

Prevention of rhinovirus and poliovirus uncoating by WIN 51711, a new antiviral drug.

WIN 51711, a potent new antipicornavirus drug, has been shown to inhibit an early event in the replication cycle of human poliovirus type 2 and human rhinovirus type 2. WIN 51711 was not virucidal and had no measurable effect on the adsorption of [3H]uridine-labeled virions to cells. When virion penetration of the plasma membrane was determined through loss of sensitivity to neutralizing antisera, WIN 51711 had no effect on poliovirus penetration, but inhibited rhinovirus penetration by 40%. In the presence of WIN 51711, exposure of neutral red-encapsidated virus-infected cells to light at 3 h postinfection resulted in a 3-log reduction in the number of infectious centers, indicating that WIN 51711 maintained the viral RNA in the encapsidated state after penetrating the cell membrane. The inhibition of uncoating by WIN 51711 in the neutral red assay was found to be concentration dependent, with a concentration of 0.03 micrograms/ml resulting in a 90% inhibition of uncoating. Sucrose gradient sedimentation of lysates from whole cells infected with [3H]uridine-labeled poliovirus showed that poliovirions remained intact in the presence of WIN 51711, but were uncoated in the absence of drug. WIN 51711 also prevented thermal inactivation of poliovirus infectivity, indicating a direct stabilizing effect of this compound on virion capsid conformation.