Infectious Bursal Disease Virus (IBDV): A Segmented Double-Stranded RNA Virus With a T=13 Capsid That Lacks a T=1 Core.
José R. Castón, José F. Rodríguez and José L. Carrascosa
from: Segmented Double-stranded RNA Viruses: Structure and Molecular Biology (Edited by: John T. Patton). Caister Academic Press, U.K. (2008)
Infectious Bursal Disease Virus (IBDV) is the best-characterized member of the family Birnaviridae. These viruses have bipartite dsRNA genomes enclosed in single-layered icosahedral capsids with T=13l geometry. IBDV shares functional strategies and structural features with many other icosahedral dsRNA viruses, except that it lacks the T=1 (or pseudo T=2) core common to the Reoviridae, Cystoviridae, and Totiviridae. Interestingly, the IBDV capsid protein exhibits structural domains that show homology to those of the capsid proteins of some positive-sense single-stranded RNA viruses, such as the nodaviruses and tetraviruses, as well as the T=13 capsid shell protein of the Reoviridae. The T=13 shell of the IBDV capsid is formed by trimers of VP2, a protein generated by removal of the C-terminal domain from its precursor, pVP2. The trimming of pVP2 is performed on immature particles as part of the maturation process. The other major structural protein, VP3, is a multifunctional component lying under the T=13 shell that influences the inherent structural polymorphism of pVP2. The virus-encoded RNA-dependent RNA polymerase, VP1, is incorporated into the capsid through its association with VP3. VP3 also interacts extensively with the viral dsRNA genome, an organization that probably contributes to virion stability. The role of pVP2 and VP3 specific sequences in capsid assembly has been studied using heterologous expression systems. Such analyses have shown that the formation of the T=13 capsid involves the interaction of an amphiphilic α-helix located at the C-terminal domain of pVP2 with a specific sequence at the C-terminus of VP3. X-ray crystallography has provided addition insight into the structure and interaction of VP2, the basic building block of IBDV particle read more ...