gamma- and deltacoronavirus non-structural protein 2 (Nsp2), similar to IBV Nsp2 and related proteins
Coronavirus non-structural proteins (Nsps) are encoded in ORF1a and ORF1b. Post infection, the genomic RNA is released into the cytoplasm of the cell and translated into two long polyproteins (pp), pp1a and pp1ab, which are then autoproteolytically cleaved by two viral proteases Nsp3 and Nsp5 into smaller subunits. Nsp2 is one of these cleaved subunits. The functions of Nsp2 remain unclear. This gamma- and deltacoronavirus family includes Avian infectious bronchitis virus (IBV) Nsp2 which has been shown to be a weak protein kinase R (PKR) antagonist, which may suggest that it plays a role in interfering with intracellular immunity. This family may be distantly related to a family of alpha- and betacoronavirus Nsp2, which includes severe acute respiratory syndrome coronavirus (SARS-CoV) Nsp2, and Murine hepatitis virus (MHV) Nsp2 (also known as p65). SARS-CoV Nsp2, rather than playing a role in viral replication, may be involved in altering the host cell environment; deletion of Nsp2 from the SARS-CoV genome results in only a modest reduction in viral titers. It has been shown to interact with two host proteins, prohibitin 1 (PHB1) and PHB2, which have been implicated in cellular functions, including cell-cycle progression, cell migration, cellular differentiation, apoptosis, and mitochondrial biogenesis. MHV Nsp2/p65, different from SARS-CoV Nsp2, may play an important role in the viral life cycle.