Identification of protease and ADP-ribose 1″-monophosphatase activities associated with transmissible gastroenteritis virus non-structural protein 3

Abstract

The replicase polyproteins, pp1a and pp1ab, of porcine Transmissible gastroenteritis virus (TGEV) have been predicted to be cleaved by viral proteases into 16 non-structural proteins (nsp). Here, enzymic activities residing in the amino-proximal region of nsp3, the largest TGEV replicase processing product, were characterized. It was shown, by in vitro translation experiments and protein sequencing, that the papain-like protease 1, PL1^pro, but not a mutant derivative containing a substitution of the presumed active-site nucleophile, Cys¹⁰⁹³, cleaves the nsp2|nsp3 site at ⁸⁷⁹Gly|Gly⁸⁸⁰. By using an antiserum raised against the pp1a/pp1ab residues 526–713, the upstream processing product, nsp2, was identified as an 85 kDa protein in TGEV-infected cells. Furthermore, PL1^pro was confirmed to be flanked at its C terminus by a domain (called X) that mediates ADP-ribose 1″-phosphatase activity. Expression and characterization of a range of bacterially expressed forms of this enzyme suggest that the active X domain comprises pp1a/pp1ab residues Asp¹³²⁰–Ser¹⁴⁸⁶.