The 3C-Like Proteinase of an Invertebrate Nidovirus Links Coronavirus and Potyvirus Homologs

AUTOR(ES)

Ziebuhr, John

FONTE

American Society for Microbiology

RESUMO

Gill-associated virus (GAV), a positive-stranded RNA virus of prawns, is the prototype of newly recognized taxa (genus Okavirus, family Roniviridae) within the order Nidovirales. In this study, a putative GAV cysteine proteinase (3C-like proteinase [3CLpro]), which is predicted to be the key enzyme involved in processing of the GAV replicase polyprotein precursors, pp1a and pp1ab, was characterized. Comparative sequence analysis indicated that, like its coronavirus homologs, 3CLpro has a three-domain organization and is flanked by hydrophobic domains. The putative 3CLpro domain including flanking regions (pp1a residues 2793 to 3143) was fused to the Escherichia coli maltose-binding protein (MBP) and, when expressed in E. coli, was found to possess N-terminal autoprocessing activity that was not dependent on the presence of the 3CLpro C-terminal domain. N-terminal sequence analysis of the processed protein revealed that cleavage occurred at the location 2827LVTHE↓VRTGN2836. The trans-processing activity of the purified recombinant 3CLpro (pp1a residues 2832 to 3126) was used to identify another cleavage site, 6441KVNHE↓LYHVA6450, in the C-terminal pp1ab region. Taken together, the data tentatively identify VxHE↓(L,V) as the substrate consensus sequence for the GAV 3CLpro. The study revealed that the GAV and potyvirus 3CLpros possess similar substrate specificities which correlate with structural similarities in their respective substrate-binding sites, identified in sequence comparisons. Analysis of the proteolytic activities of MBP-3CLpro fusion proteins carrying replacements of putative active-site residues provided evidence that, in contrast to most other 3C/3CLpros but in common with coronavirus 3CLpros, the GAV 3CLpro employs a Cys2968-His2879 catalytic dyad. The properties of the GAV 3CLpro define a novel RNA virus proteinase variant that bridges the gap between the distantly related chymotrypsin-like cysteine proteinases of coronaviruses and potyviruses.

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