Bactrian camel (Camelus bactrianus) integrins alphavbeta3 and alphavbeta6 as FMDV receptors: molecular cloning, sequence analysis and comparison with other species.

Integrins are heterodimeric adhesion receptors that participate in a variety of cell-cell and cell-extracellular matrix protein interactions. Many integrins recognize RGD sequences displayed on extracellular matrix proteins and the exposed loops of viral capsid proteins. Four members of the alphav integrin family of cellular receptors, alphavbeta3, alphavbeta6, alphavbeta1 and alphavbeta8, have been identified as receptors for foot-and-mouth disease virus (FMDV) in vitro, and integrins are believed to be the receptors used to target epithelial cells in the infected animals. To analyse the roles of the alphav integrins from a susceptible species as viral receptors, we have cloned Bactrian camel alphav, beta3 and beta6 integrin cDNAs and compared them to those of other species. The coding sequences for Bactrian camel integrin alphav, beta3 and beta6 were found to be 3165, 2289 and 2367 nucleotides in length, encoding 1054, 762 and 788 amino acids, respectively. The Bactrian camel alphav, beta3 and beta6 subunits share many structural features with homologues of other species, including the ligand binding domain and cysteine-rich region. Phylogenetic trees and similarity analyses showed the close relationships of integrin genes from Bactrian camels, pigs and cattle, which are each susceptible to FMDV infection, that were distinct from the orders Rodentia, Primates, Perissodactyla, Carnivora, Galliformes and Xenopus. We postulate that host tropism of FMDV may in part be related to the divergence in integrin subunits among different species.