Poliovirus type 1/type 3 antigenic hybrid virus constructed in vitro elicits type 1 and type 3 neutralizing antibodies in rabbits and monkeys

Addition of a foreign oligopeptide to the major capsid protein of poliovirus

Insertion mutants of type 3 poliovirus (Sabin strain) were constructed that encode additional amino acid sequences at the level of residue 100 of the capsid polypeptide VP1 within the neutralization site 1, corresponding to a loop on the capsid surface. The addition of a tri- or hexapeptide did not hamper virus viability. The antigenic pattern of insertion mutants was only modified locally: all mutants lost reactivity of neutralization site 1 with the corresponding monoclonal antibodies, while the reactivity of sites 2 and 3 was unaffected by the insertion. We have shown for one of the mutants--vFG68--that the antigenic specificity of the neutralization site 1 was replaced by a new one. Although vFG68 differs from its parental Sabin strain only by the addition of three amino acids within VP1, neutralizing antibodies specific for vFG68 were induced by the native virion as well as by the heat-denatured mutated virions. Our results demonstrate that an oligopeptide of three or six amino acids can lengthen VP1 at the level of antigenic site 1 without affecting virus multiplication and that this foreign peptide is exposed on the virion surface.

Mutational analysis of the genome-linked protein VPg of poliovirus

Using a mutagenesis cartridge (R. J. Kuhn, H. Tada, M. F. Ypma-Wong, J. J. Dunn, B. L. Semler, and E. Wimmer, Proc. Natl. Acad. Sci. USA 85:519-523, 1988), we have generated single and multiple amino acid replacement mutants, as well as a single amino acid insertion mutant in the genome-linked protein VPg of poliovirus. Moreover, we constructed three different 5-amino-acid insertion mutants that map close to the C terminus of 3A, a viral polypeptide whose coding sequence is adjacent to VPg. Transfection of HeLa cells with RNA synthesized in vitro was used to test the effect of the mutation on viral proliferation. Mutations were either lethal or nonlethal. A temperature-sensitive phenotype was not observed. The arginine at position 17 of VPg could not be exchanged with any other amino acid without loss of viability, whereas the lysine at position 20, an amino acid conserved among all known polioviruses, coxsackieviruses, and echoviruses, was replaceable with several neutral amino acids and even with glutamic acid. Replacement of poliovirus VPg with echovirus 9 VPg yielded viable virus with impaired growth properties. Our results suggest considerable flexibility in the amino acid sequence of a functional VPg. All insertions in polypeptide 3A proved to be lethal. In vitro translation of mutated viral RNAs gave patterns of proteolytic processing that in some cases was aberrant, even though the mutation was nonlethal.

Poliovirus host range is determined by a short amino acid sequence in neutralization antigenic site I

The mouse-adapted strain of poliovirus type 2 (Lansing) induces fatal poliomyelitis in mice after intracerebral inoculation, whereas mice inoculated with poliovirus type 1 (Mahoney) show no signs of disease. Previous work indicated that the adaptation to mouse virulence is associated with the viral capsid proteins and that mutations in neutralization antigenic site I of poliovirus reduce neurovirulence of the Lansing strain in mice. The role of antigenic site I in mouse neurovirulence was further explored by constructing an antigenic hybrid virus. Six amino acids in antigenic site I of the Mahoney strain were replaced with a sequence specific for the Lansing strain by using a mutagenesis cartridge. The hybrid virus was neutralized by polyclonal antisera elicited by the type 1 and type 2 strains of poliovirus and by neutralizing monoclonal antibodies directed against antigenic site I of type 2 virus. The hybrid virus induced paralytic disease in mice, an observation demonstrating that a short sequence of amino acids in antigenic site I is an important determinant of poliovirus host range. Antigenic site I may be involved in attachment of poliovirus to cells of the mouse central nervous system.