The full-length nsp2 replicase contributes to viral assembly in highly pathogenic PRRSV-2

ABSTRACT Porcine reproductive and respiratory syndrome viruses (PRRSVs) are significant pathogens that affect the global swine industry. Its virions consist of a central core composed of nucleocapsid (N) protein, surrounded by multiple distinct viral envelope proteins. However, the mechanisms underlying the recognition and packaging of N protein by viral envelope proteins remain elusive. In this study, we elucidated the role of nonstructural protein 2 (nsp2) from highly pathogenic PRRSV-2 (HP-PRRSV-2) in viral assembly. Firstly, among all the tested envelope proteins, only glycoprotein 5 (GP5) exhibits limited interaction with N protein. Interestingly, we demonstrated that full-length nsp2 co-immunoprecipitates (Co-IPs) with the N protein and all tested viral envelope proteins. In the presence of full-length nsp2, the N protein interacts with distinct viral envelope proteins. Moreover, upon viral infection, Co-IP experiments using nsp2-specific antibodies or N-specific antibodies revealed the formation of a complex between N and nsp2 with the M protein, GP2a, and GP5. However, neither of the two short forms of nsp2—namely nsp2TF nor nsp2N—participates in this process as they fail to interact with the N protein. Finally, our results demonstrate that this process occurs in the endoplasmic reticulum (ER) and the ER-Golgi intermediate compartment (ERGIC). Overall, our findings unveil a novel functional role for full-length nsp2 of HP-PRRSV-2 in facilitating the assembly of the N protein with viral envelope proteins. IMPORTANCE The virus assembly process of arteriviruses remains largely elusive, including the direct interaction between N protein and viral envelope proteins or the potential requirement for additional proteins in facilitating assembly. Moreover, where the N protein assembles with viral envelope proteins during the virus lifecycle remains unclear. This study reveals a novel role for nonstructural protein 2 (nsp2) in highly pathogenic porcine reproductive and respiratory syndrome virus type 2 (HP-PRRSV-2), highlighting its involvement in HP-PRRSV-2 assembly. These findings provide crucial insights into HP-PRRSV-2 assembly and enhance our understanding of their lifecycle. Overall, this study offers an alternative approach to developing a new antiviral strategy targeting PRRSV-2 assembly.