Isoelectric focusing and 2D-analysis of poliovirus proteins

A new antigenic site of poliovirus recognized by an intertypic cross-neutralizing monoclonal antibody

A monoclonal antibody (mAb 7J6) neutralizing poliovirus type 2 (PV2) and poliovirus type 1 (PV1) was obtained after immunization of BALB/c mice with infectious PV2, strain MEF-1. Preincubation of mAb 7J6 with PV1 inhibited its binding to PV2 and vice versa. Neutralization-resistant variants of PV2 and PV1 were selected. Nucleotide sequencing of the RNAs of some variants revealed mutations in the loop of amino acid residues 239 to 245 in VP2 and in the loop of amino acid residues 195 to 207 in VP3. This is the first evidence that these two loops contribute to a neutralization antigenic site (N-Ag) for poliovirus. Moreover, this new site on PV2 induced intertypic cross-neutralizing antibodies.

pH 2 instability of a mutant of mengovirus is related to its interferon sensitivity

The is-1 mutant of mengovirus is 100 times more sensitive to interferon (IFN) than wild type, as measured by a yield reduction assay in the G3 line of mouse L cells, and is also much more readily inactivated at pH 2. Neither isolated nor encapsidated RNA is degraded under these conditions, which suggests that the pH-sensitive region resides on the virus coat. One-third of the viruses selected for resistance to low pH also showed enhanced resistance to IFN. Attempts to isolate IFN resistant strains directly from is-1 stocks were unsuccessful. These results suggest that either a capsid protein or its precursor is an active anti-IFN agent.

Molecular basis for linkage of a continuous and discontinuous neutralization epitope on the structural polypeptide VP2 of poliovirus type 1

We obtained neutralizing monoclonal antibodies against a continuous neutralization epitope on VP2 of poliovirus type 1 strain Mahoney by using a combined in vivo-in vitro immunization procedure. The antibody-binding site was mapped to amino acid residues within the peptide segment (residues 164 through 170) of VP2 by competition with synthetic peptide and sequencing of resistant mutants. Cross-neutralization of these mutants with another neutralizing monoclonal antibody revealed a linkage of the continuous epitope and a discontinuous neutralization epitope involving both loops of the double-loop structure of VP2 at the twofold axis on the surface of the virion.

N-AgIB of poliovirus type 1: a discontinuous epitope formed by two loops of VP1 comprising residues 96-104 and 141-152

Analysis of resistant mutants to neutralizing monoclonal antibodies revealed a discontinuous neutralization epitope on VP1 of poliovirus type 1, Mahoney. The epitope has the unique property of being also part of a sequential epitope within neutralization antigenic site I (N-AgI). It is formed by residues in the loop 96-104 connecting the B and C strand and in the loop 141-152 connecting the D and E strand of VP1. Because of strong analogy to neutralization immunogen IB (NImIB) of human rhinovirus 14 (HRV-14) we have called this site N-AgIB of poliovirus type 1.

Evidence for a complex structure of neutralization antigenic site I of poliovirus type 1 Mahoney

We have selected neutralization escape mutants by using a monoclonal antibody (nt-MAb) against a sequential epitope between amino acids 93 through 104 (neutralization antigenic site I) of poliovirus type 1 Mahoney. The majority of mutants were also resistant against five strain-specific nt-MAbs which recognized conformation-dependent epitopes, suggesting that the neutralization antigenic site I must be involved in the formation of such epitopes. An analysis of all mutants by the binding of nt-MAbs and by isoelectric focusing of VP1 allowed discrimination of five classes of mutants. Sequence analysis of mutant RNAs revealed point mutations and deletions in the antibody-binding site.

Guanidine-resistant poliovirus mutants produce modified 37-kilodalton proteins

Eighteen spontaneous, guanidine-resistant mutants of poliovirus were obtained by plaque selection. Isoelectric focusing demonstrated charge changes in a 37-kilodalton protein, pX, among three of the mutants. The precursor of pX, NCVP5b , also exhibited charge changes among the three mutants. pX of 12 mutants was also examined by peptide mapping with Staphylococcus aureus V8 protease. Nine of the mutants presented modified maps, and seven of these maps were identical. The demonstration of mutational changes in pX in 12 of 18 mutants suggests a role for this protein in determining the guanidine trait of poliovirus and corroborates studies with foot-and-mouth disease virus.

Rapid analytical and preparative separation of structural polypeptides of poliovirus by reverse-phase high-performance liquid chromatography

A reverse-phase high-performance liquid-chromatography (RP-HPLC) technique was developed for rapid (20 min) and effective separation of the structural polypeptides of poliovirus of strains of all three serological types. The method is useful for quantitative analysis as well as for isolation of polypeptides on a micropreparative scale for chemical, biochemical and immunological studies. All four virus polypeptides (VP1 to VP4) were obtained quantitatively in high purity by this one-step procedure. The solvents used were volatile and easily removed by evaporation, giving dry, amorphous polypeptides free of any additives. The separation mechanism of this RP-HPLC is based on the hydrophobicity of the protein surface. It is distinct from other separation methods such as molecular sieving and isoelectric focusing. Therefore, differences in primary and secondary structure of a polypeptide can be detected by RP-HPLC.

Picornaviral structure and assembly

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Two-dimensional electrophoretic analysis of encephalomyocarditis viral proteins

All four capsid proteins of encephalomyocarditis virus and the precursor to two of these were resolved from purified virions with two-dimensional gel electrophoresis. In addition, all of the known stable virus-specific proteins found in infected cells, but not the primary and intermediate precursor proteins, could be resolved with these techniques.

Isoelectric focusing of viral polypeptides in urea. A methodological study on poliovirus

The applicability of isoelectric focusing in urea to the analysis of viral polypeptides is reported, using poliovirus as a model. Experimental techniques for the dissociation of virus particles, for isoelectric focusing in urea-containing polyacrylamide gels (rods, flat bed and slab gels) and for pH measurement and two-dimensional analysis are described and their results, as applied to poliovirus polypeptides, discussed. Special attention is given to problems of recovery of all of the proteins and the incidence of artifacts. The influence of reagents, dissociation conditions, focusing procedures and preparation and storage of virus material on the occurrence of charge modifications of the polypeptides has been investigated. Some recommendations are made for the application of the method to other viruses of particles.