Foot-and-mouth disease virus is a ligand for the high-affinity binding conformation of integrin alpha5beta1: influence of the leucine residue within the RGDL motif on selectivity of integrin binding

Field isolates of foot-and-mouth disease virus (FMDV) use RGD-dependent integrins as receptors for internalization, whereas strains that are adapted for growth in cultured cell lines appear to be able to use alternative receptors like heparan sulphate proteoglycans (HSPG). The ligand-binding potential of integrins is regulated by changes in the conformation of their ectodomains and the ligand-binding state would be expected to be an important determinant of tropism for viruses that use integrins as cellular receptors. Currently, alphavbeta3 is the only integrin that has been shown to act as a receptor for FMDV. In this study, a solid-phase receptor-binding assay has been used to characterize the binding of FMDV to purified preparations of the human integrin alpha5beta1, in the absence of HSPG and other RGD-binding integrins. In this assay, binding of FMDV resembled authentic ligand binding to alpha5beta1 in its dependence on divalent cations and specific inhibition by RGD peptides. Most importantly, binding was found to be critically dependent on the conformation of the integrin, as virus bound only after induction of the high-affinity ligand-binding state. In addition, the identity of the amino acid residue immediately following the RGD motif is shown to influence differentially the ability of FMDV to bind integrins alpha5beta1 and alphavbeta3 and evidence is provided that alpha5beta1 might be an important FMDV receptor in vivo.