Journal:PLoS ONE:1

Antiviral Activity of 3(2H)- and 6-Chloro-3(2H)-Isoflavenes against Highly Diverged, Neurovirulent Vaccine-Derived, Type2 Poliovirus Sewage Isolates

Lester M. Shulman, Danit Sofer, Yossi Manor, Ella Mendelson, Jean Balanant, Anna Laura Salvati, Francis Delpeyroux, Lucia Fiore^[1]

Molecular Tour

Complete Poliovirus 2 Virion (capsid) based on PDB entry 1eah, example of 3-fold symmetry is in red, example of 5-fold symmetry is in blue

Poliovirus is a member of the Picornaviridae. Like other members of the Picornaviridae, poliovirus RNA is encapsulated in an icosahedral structure (see the static image at the left or simplified model of capsid) formed from 60 capsomeres with axes of five-fold and three-fold symmetry. So, each capsomer participates in formation of both kinds of symmetry. A single capsomer contains one copy of viral capsid proteins VP1 (light blue), VP2 (pale green), VP3 (light orange) and VP4 (light magenta). The binding site for the human poliovirus receptor is located in a canyon at the five-fold axis of symmetry (external viewpoint). The VP1 of picornaviruses contain a hydrophobic pocket that is accessed through this canyon. This pocket is normally occupied by pocket factors, sphingosine-like molecules including palmitic and myristic acids and hydrophobic compounds, that stabilize the capsid and whose removal is a necessary prerequisite for uncoating. The broad-spectrum antiviral agent SCH48973 is observed binding in a pocket within the beta-barrel of VP1, in approximately the same location that natural pocket factors bind to polioviruses (1eah). SCH48973 forms predominantly hydrophobic interactions with the pocket residues. Flavanoids and flavonoids were shown to have antiviral activity in vitro against several picornaviruses including type 2 polioviruses. These compounds act primarily by occupying the hydrophobic pocket, thus interfering with virus uncoating. Compounds 3(2H)-Isoflavene (C2) and 6-chloro-3(2H)-Isoflavene (C10) are relatively similar to SCH48973 and exert their antiviral effect by interacting with amino acids in the viral capsid pockets. Ambiguous vaccine-derived poliovirus 2 (aVDPV) isolate SD-06-10 was resistant to the antiviral effects of both C2 and C10 compounds. The in silico translated amino acid sequences of the capsid proteins of all of the aVDPV2 isolates and Sabin 2 (AY184220) were compared and amino acid substitutions in capsid proteins that were unique to SD-06-10 were determined. The positions of these unique substitutions were mapped onto the coordinates of type 2 poliovirus (1eah) using PyMOL and are represented by red spheres. The hydrophobic pocket is represented by blue spheres and the position of amino-acid substitutions that were previously shown to result in loss of sensitivity (yellow) to or dependence on isoflavenes are indicated by the yellow and green spheres, respectively. One unique substitution at amino acid Ser6 of VP3, was located in the central junction of the 5 capsomeres at the 5-fold axis of symmetry (click to enlarge) and another unique substitution at Ser206 of VP3, was located adjacent to the 3-fold axis of symmetry where they might influence capsid flexibility and or stability. The positions of unique substitutions of SD-07-03 was also determined and were mapped onto the coordinates of type 2 poliovirus and are represented by red spheres. The hydrophobic pocket is represented by blue spheres and the position of amino acid 143 of VP1, one of two determinants for neurovirulence in type 2 poliovirus is represented by orange spheres. The colors are as in the previous scenes. Three substitutions are located adjacent to the 5-fold axis of symmetry. Unique substitutions found in SD-07-03 at residues 141, 144, and 145 of VP1 flank Thr143. None of SD-0703’s unique substitutions were located near the 3-fold axis of symmetry.