Birnavirus Ribonucleoprotein Assembly

The interaction of the structural VP3 polypeptide of infectious bursal disease virus (IBDV) with virus-encoded dsRNA is essential both for the assembly of ribonucleoprotein complexes responsible for genome transcription and replication and for the evasion of hosts antiviral responses. Surface plasmon resonance analysis allowed us to determine the kinetic constants of the VP3-dsRNA interaction as well as to map the VP3 dsRNA bipartite dsRNA binding domain (dsRBD), uncovering the specific role of the previously described Patch1 and Patch2 dsRB subdomains. Here we show that the Patch1 domain plays a primary binding function while Patch2 exerts a subordinate role stabilizing VP3-dsRNA complexes. The use of a set of VP3 mutant versions facilitated the identification of K99 and K106 within Patch1 as the essential residues for the formation of VP3-dsRNA complexes. Furthermore, replacement of either one of these two residues by aspartic acid completely thwarts both evasion from hosts sensors and virus replication. Data presented here allow us to propose a VP3-dsRNA interaction model that should help to further elucidate the mechanics of IBDV morphogenesis and genome packaging as well as to better understand how VP3 counteracts recognition of virus-encoded dsRNA by specialized hosts sensors.