PCV2

PCV2 is a small, non-enveloped virus containing a single-stranded, circular DNA genome. PCV2 is identified as the dominant pathogen causing postweaning multisystemic wasting syndrome (PMWS) and a number of associated diseases in pigs. Notably, PCV2 capsid protein (233/234 amino acids) encoded by the open reading frame 2 (ORF2) of PCV2 is capable of self-assembly into VLP and resembling the icosahedral morphology of the native PCV2 virions.

Replication-associated protein(Q8BB16)

Function

Essential for the replication of viral ssDNA. The closed circular ssDNA genome is first converted to a superhelical dsDNA. Rep and/or Rep' binds a specific hairpin at the genome origin of replication. Introduces an endonucleolytic nick within the conserved sequence 5'-AGTATTAC-3' in the intergenic region of the genome, thereby initiating the rolling circle replication (RCR). Following cleavage, binds covalently to the 5'-phosphate of DNA as a tyrosyl ester. The cleavage gives rise to a free 3'-OH that serves as a primer for the cellular DNA polymerase. The polymerase synthesizes the (+) strand DNA by rolling circle mechanism. After one round of replication, a Rep-catalyzed nucleotidyl transfer reaction releases a circular single-stranded virus genome, thereby terminating the replication. Displays origin-specific DNA cleavage, and nucleotidyl transferase.

Capsid protein(O56129)

Function

Self-assembles to form the virion icosahedral capsid with a T=1 symmetry. This very small capsid (17 - 22 nm in diameter) allows the virus to be very stable in the environment and resistant to some disinfectants, including detergents. Essential for the initial attachment to heparan sulfate moieties and chondroitin sulfate B of the host cell surface proteoglycans. After attachment, the virus is internalized in a clathrin-, caveolae- and dynamin-independent, actin and Rho-GTPase-mediated pathway and traffics to the nucleus. The capsid protein binds and transports the viral genome and Rep across the nuclear envelope (By similarity).

Protein NS0 (Q8BB12)

Function

May play a role inhost modulation. Is not involved in viral protein synthesis or DNA replication.

Protein ORF3 (O56124)

Function

Plays a role in modulating host cell signaling by binding to and degrading host RGS16.Not necessary for virus replication.

Anti-apoptotic ORF4 protein (O56125)

Function

Antagonizes host cell apoptosis by interacting with host ferritin heavy chain. The ORF4 protein physically binds host FHC, resulting in the reduction of FHC protein levels in host cells. Reduction of FHC concentration further inhibits the accumulation of reactive oxygen in host cells, leading to reduced apoptosis.

Reference:

1.Mo X, Li X, Yin B, Deng J, Tian K, Yuan A. Structural roles of PCV2 capsid protein N-terminus in PCV2 particle assembly and identification of PCV2 type-specific neutralizing epitope. PLoS Pathog. 2019 Mar 1;15(3):e1007562. doi: 10.1371/journal.ppat.1007562. PMID: 30822338; PMCID: PMC6415871.

2.Meng XJ (2013) Porcine circovirus type 2 (PCV2): pathogenesis and interaction with the immune system. Annu Rev Anim Biosci 1: 43–64. 10.1146/annurev-animal-031412-103720

3.Yin S, Sun S, Yang S, Shang Y, Cai X, et al. (2010) Self-assembly of virus-like particles of porcine circovirus type 2 capsid protein expressed from Escherichia coli. Virol J 7: 166 10.1186/1743-422X-7-166

4.Chae C (2005) A review of porcine circovirus 2-associated syndromes and diseases. Vet J 169: 326–336. 10.1016/j.tvjl.2004.01.012

5.Rosell C, Segales J, Ramos-Vara JA, Folch JM, Rodriguez-Arrioja GM, et al. (2000) Identification of porcine circovirus in tissues of pigs with porcine dermatitis and nephropathy syndrome. Vet Rec 146: 40–43.