Abstract:
Field isolates of foot-and-mouth disease viruses (FMDVs) utilize integrin-mediated cell entry
but many, including Southern African Territories (SAT) viruses, are difficult to adapt to BHK-
21 cells, thus hampering large-scale propagation of vaccine antigen. However, FMDVs
acquire the ability to bind to cell surface heparan sulphate proteoglycans, following serial
cytolytic infections in cell culture, likely by the selection of rapidly replicating FMDV variants.
In this study, fourteen SAT1 and SAT2 viruses, serially passaged in BHK-21 cells, were virulent
in CHO-K1 cells and displayed enhanced affinity for heparan, as opposed to their lowpassage
counterparts. Comparative sequence analysis revealed the fixation of positively
charged residues clustered close to the icosahedral 5-fold axes of the virus, at amino acid
positions 83–85 in the βD-βE loop and 110–112 in the βF-βG loop of VP1 upon adaptation
to cultured cells. Molecular docking simulations confirmed enhanced binding of heparan sulphate
to a model of the adapted SAT1 virus, with the region around VP1 arginine 112 contributing
the most to binding. Using this information, eight chimeric field strain mutant
viruses were constructed with additional positive charges in repeated clusters on the virion
surface. Five of these bound heparan sulphate with expanded cell tropism, which should
facilitate large-scale propagation. However, only positively charged residues at position
110–112 of VP1 enhanced infectivity of BHK-21 cells. The symmetrical arrangement of
even a single amino acid residue in the FMD virion is a powerful strategy enabling the virus
to generate novel receptor binding and alternative host-cell interactions.
