title: The arterivirus Nsp2 protease. An unusual cysteine protease with primary structure similarities to both papain-like and chymotrypsin-like proteases.
abstract: The replicase ORF1a polyprotein of equine arteritis virus, a positive-stranded RNA virus, is proteolytically processed into (at least) six nonstructural proteins (Nsp). A papain-like Cys protease in Nsp1 and a chymotrypsin-like Ser protease in Nsp4 are involved in this process. In this paper we demonstrate that the Nsp2/3 junction is not cleaved by either of these previously described proteases. Comparative sequence analysis suggested that an additional Cys protease resided in the N-terminal Nsp2 domain. For equine arteritis virus, this domain was shown to induce Nsp2/3 cleavage in a trans-cleavage assay. Processing was abolished when the putative active site residues, Cys-270 and His-332, were replaced. Other Nsp2 domains and three other conserved Cys residues were also shown to be essential. The Nsp2 Cys protease displays sequence similarity with viral papain-like proteases. However, the presumed catalytic Cys-270 is followed by a conserved Gly rather than the characteristic Trp. Replacement of Gly-271 by Trp abolished the Nsp2/3 cleavage. Conservation of a Cys-Gly dipeptide is a hallmark of viral chymotrypsin-like Cys proteases. Thus, the arterivirus Nsp2 protease is an unusual Cys protease with amino acid sequence similarities to both papain-like and chymotrypsin-like proteases.
authors.affiliation: Department of Virology, Faculty of Medicine, Leiden University, The Netherlands.
authors.forename: E J
authors.initials: EJ
authors.lastname: Snijder
authors.forename: A L
authors.initials: AL
authors.lastname: Wassenaar
authors.forename: W J
authors.initials: WJ
authors.lastname: Spaan
authors.forename: A E
authors.initials: AE
authors.lastname: Gorbalenya
mesh_terms: D000595:Amino Acid Sequence; D018018:Arterivirus / Q000201:enzymology*; D002918:Chymotrypsin / Q000737:chemistry*; D003546:Cysteine Endopeptidases / Q000737:chemistry*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010206:Papain / Q000737:chemistry*
chemical_list: D002918:Chymotrypsin; D003546:Cysteine Endopeptidases; C078306:nsP2 proteinase; D010206:Papain