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The Crystal Structure of Porcine Reproductive and Respiratory Syndrome Virus Nonstructural Protein Nsp1β Reveals a Novel Metal-Dependent Nuclease

ABSTRACT Porcine reproductive and respiratory syndrome virus (PRRSV), a member of the Arteriviridae family of Nidovirales, is the causative agent of porcine reproductive and respiratory syndrome, which results in enormous economic losses in the swine industry. As the second protein encoded by the PRRSV genome, nsp1β cleaves itself from the downstream nsp2 protein via a C-terminal papain-like cysteine protease (PCP) domain. Although nsp1β is known to be involved in virulence, its precise role in the process of viral infection remains unclear. In this work, we describe the homodimeric crystal structure of PRRSV nsp1β in its natural, self-processed form. We show that the architecture of its N-terminal domain (NTD) adopts a fold closely resembling that of several known nucleases and has intrinsic nuclease activity that is strongly activated by manganese ions in vitro. Key features, however, distinguish nsp1β from characterized nucleases, including the C-terminal PCP domain (which is responsible for the self-release of nsp1β from nsp2), a linker domain (LKD) that connects the NTD and the PCP domain, and a C-terminal extension (CTE) that binds to and is stabilized by the putative substrate binding site of the PCPβ domain. Combined with the reported nuclear localization of this protein, these results shed light on the self-processing mode and precise biological function of nsp1β and thus offer a multitarget template for future drug discovery.