The capsid protein of infectious bursal disease virus contains a functional α4β1 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 α4β1 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 α4β1 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 α4β1 integrin as a specific binding receptor in avian cells.