The papain-like protease of avian infectious bronchitis virus has deubiquitinating activity

Abstract

Coronavirus papain-like proteases (PLPs) can act as proteases that process virus-encoded large replicase polyproteins and also as deubiquitinating (DUB) enzymes. Like the PLPs of other coronaviruses (CoVs), the avian infectious bronchitis virus (IBV) PLP catalyzes proteolysis of Gly-Gly dipeptide bonds to release mature cleavage products. However, the other functions of the IBV PLP are not well understood. In this study, we found that IBV exhibits strong global DUB activity with significant reductions of the levels of ubiquitin (Ub)-, K48-, and K63-conjugated proteins. The DUB activity exhibited a clear time dependence, with stronger DUB activity in the early stage of viral infection. Furthermore, the IBV replicase-encoded PLP, including the downstream transmembrane (TM) domain, is a DUB enzyme and dramatically reduced the level of Ub-conjugated proteins, while processing both K48- and K63-linked polyubiquitin chains. By contrast, PLP did not cause any reduction of haemagglutinin (HA)-Ub-conjugated proteins. In addition, mutations of the catalytic residues of PLP-TM, Cys1274Ser and His1437Lys, reduced DUB activity against Ub-, K48- and K63- conjugated proteins, indicating that the DUB activity of the PLP-TM wild-type protein is not completely dependent on its catalytic activity. Overall, these results demonstrate that the IBV-encoded PLP-TM functions as a DUB enzyme and suggest that IBV may interfere with the activation of host antiviral signaling pathway by degrading polyubiquitin-associated proteins.

Post-Translational Modifications of Coronavirus Proteins: Roles and Function

“…Deubiquitinating activity of coronavirus PLPro Coronavirus encodes one or two PLPro in the nsp3, which carry out the proteolytic cleavage that releases nsp1, nsp2 and nsp3 from the polyprotein [15,173,174]. Apart from its protease activity, SARS-CoV PLPro was also shown to possess deubiquitinating (DUB) activity [175,176], which was also identified later for PLP2 of HCoV-NL63 [177] and MHV-A59 [178], as well as PLPro of MERS-CoV [179,180] and IBV [181]. Structural studies revealed that SARS-CoV PLPro shared similar fold with known DUB enzymes, but exhibited several distinct features [182].…”

Structure and Function of Viral Deubiquitinating Enzymes

“…IBV PL pro was found to cleave the polyprotein between Gly-Gly residues at two sites, releasing nsp2 and nsp3 [184][185][186][187]. It adopts a fold common to USP DUBs and possesses an N-terminal UBL domain seen in most other CoV PL pro domains [188], and it cleaves Lys48-and Lys63-linked polyUb chains [189], with an apparent preference for Lys63 linkages [188]. While DUB activity of IBV PL pro has been demonstrated, the importance of this function has not been established.…”

Gga-miR-30d regulates infectious bronchitis virus infection by targeting USP47 in HD11 cells

“…Coronavirus, for instance MHV-A59, SARS-CoV, HCoV-NL63 [29][30][31], encode the protein with deubiquitinating activity to promote viral infection. Similarly, as one of Coronavirus, it was reported that IBV-encoded PLP-TM functions as a DUB enzyme, which significant reduced the levels of ubiquitin (Ub)-, K48-, and K63-conjugated proteins in the early stage of viral infection [32]. By degrading polyubiquitin chains associated with ubiquitin proteins, IBV PLP-TM may prevent the activation of host antiviral signaling pathways to escapes host antiviral immune system.…”