Infectious Bursal Disease Virus (IBDV) VP3

Full Name

Function

Capsid protein VP2 self assembles to form an icosahedral capsid with a T=13 symmetry, about 70 nm in diameter, and consisting of 260 VP2 trimers. The capsid encapsulates the genomic dsRNA. VP2 is also involved in attachment and entry into the host cell by interacting with host ITGA4/ITGB1.
Capsid protein VP3 plays a key role in virion assembly by providing a scaffold for the capsid made of VP2. May self-assemble to form a T=4-like icosahedral inner-capsid composed of at least 180 trimers. Plays a role in genomic RNA packaging by recruiting VP1 into the capsid and interacting with the dsRNA genome segments to form a ribonucleoprotein complex. Additionally, the interaction of the VP3 C-terminal tail with VP1 removes the inherent structural blockade of the polymerase active site. Thus, VP3 can also function as a transcriptional activator.
Protease VP4 is a serine protease that cleaves the polyprotein into its final products. Pre-VP2 is first partially cleaved, and may be completely processed by VP4 upon capsid maturation.
Structural peptide 1 is a small peptide derived from pre-VP2 C-terminus. It destabilizes and perforates cell membranes, suggesting a role during entry.
Structural peptide 2 is a small peptide derived from pre-VP2 C-terminus. It is not essential for the virus viability, but viral growth is affected when missing.
Structural peptide 3 is a small peptide derived from pre-VP2 C-terminus. It is not essential for the virus viability, but viral growth is affected when missing.
The precursor of VP2 plays an important role in capsid assembly. First, pre-VP2 and VP2 oligomers assemble to form a procapsid. Then, the pre-VP2 intermediates may be processed into VP2 proteins by proteolytic cleavage mediated by VP4 to obtain the mature virion. The final capsid is composed of pentamers and hexamers but VP2 has a natural tendency to assemble into all-pentameric structures. Therefore pre-VP2 may be required to allow formation of the hexameric structures.

Cellular Location

Cytoplasm; Host cytoplasm; Virion