title: Structure and cleavage specificity of the chymotrypsin-like serine protease (3CLSP/nsp4) of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV).
abstract: Biogenesis and replication of the porcine reproductive and respiratory syndrome virus (PRRSV) include the crucial step of replicative polyprotein processing by self-encoded proteases. Whole genome bioinformatics analysis suggests that nonstructural protein 4 (nsp4) is a 3C-like serine protease (3CLSP), responsible for most of the nonstructural protein processing. The gene encoding this protease was cloned and expressed in Escherichia coli in order to confirm this prediction. The purified protein was crystallized, and the structure was solved at 1.9 A resolution. In addition, the crystal structure of the Ser118Ala mutant was determined at 2.0 A resolution. The monomeric enzyme folds into three domains, similar to that of the homologous protease of equine arteritis virus, which, like PRRSV, is a member of the family Arteriviridae in the order of Nidovirales. The active site of the PRRSV 3CLSP is located between domains I and II and harbors a canonical catalytic triad comprising Ser118, His39, and Asp64. The structure also shows an atypical oxyanion hole and a partially collapsed S1 specificity pocket. The proteolytic activity of the purified protein was assessed in vitro. Three sites joining nonstructural protein domains in the PRRSV replicative polyprotein are confirmed to be processed by the enzyme. Two of them, the nsp3/nsp4 and nsp11/nsp12 junctions, are shown to be cleaved in trans, while cis cleavage is demonstrated for the nsp4/nsp5 linker. Thus, we provide structural evidence as well as enzymatic proof of the nsp4 protein being a functional 3CLSP. We also show that the enzyme has a strong preference for glutamic acid at the P1 position of the substrate.
authors: CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China.
authors: Xinsheng
authors: X
authors: Tian
authors: Guangwen
authors: G
authors: Lu
authors: Feng
authors: F
authors: Gao
authors: Hao
authors: H
authors: Peng
authors: Youjun
authors: Y
authors: Feng
authors: Guangpeng
authors: G
authors: Ma
authors: Mark
authors: M
authors: Bartlam
authors: Kegong
authors: K
authors: Tian
authors: Jinghua
authors: J
authors: Yan
authors: Rolf
authors: R
authors: Hilgenfeld
authors: George F
authors: GF
authors: Gao
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020134:Catalytic Domain; D002918:Chymotrypsin / Q000737:chemistry; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019316:Porcine respiratory and reproductive syndrome virus / Q000201:enzymology*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014764:Viral Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D011994:Recombinant Proteins; D014764:Viral Proteins; D012697:Serine Endopeptidases; D002918:Chymotrypsin