The capsid protein of infectious bursal disease virus contains a functional alpha 4 beta 1 integrin ligand motif.

Infectious bursal disease virus (IBDV), a member of the dsRNA Birnaviridae family, is an important immunosuppressive avian pathogen. We have identified a strictly conserved amino acid triplet matching the consensus sequence used by fibronectin to bind the alpha 4 beta 1 integrin within the protruding domain of the IBDV capsid polypeptide. We show that a single point mutation on this triplet abolishes the cell-binding activity of IBDV-derived subviral particles (SVP), and abrogates the recovering of infectious IBDV by reverse genetics without affecting the overall SVP architecture. Additionally, we demonstrate that the presence of the alpha 4 beta 1 heterodimer is a critical determinant for the susceptibility of murine BALB/c 3T3 cells to IBDV binding and infectivity. Our data suggests that the IBDV might also use the alpha 4 beta 1 integrin as a specific binding receptor in avian cells.