Abstract
Translation of foot-and-mouth disease virus RNA initiates at one of two start codons leading to the synthesis of two forms of leader proteinase Lpro (Labpro and Lbpro). These forms free themselves from the viral polyprotein by intra- and intermolecular self-processing and subsequently cleave the cellular eukaryotic initiation factor (eIF) 4G. During infection, Lbpro removes six residues from its own C-terminus, generating sLbpro. We present the structure of sLbpro bound to the inhibitor E64-R-P-NH2, illustrating how sLbpro can cleave between Lys/Gly and Gly/Arg pairs. In intermolecular cleavage on polyprotein substrates, Lbpro was unaffected by P1 or P1′ substitutions and processed a substrate containing nine eIF4GI cleavage site residues whereas sLbpro failed to cleave the eIF4GI containing substrate and cleaved appreciably more slowly on mutated substrates. Introduction of 70 eIF4GI residues bearing the Lbpro binding site restored cleavage. These data imply that Lbpro and sLbpro may have different functions in infected cells.
Highlights
Encoded proteinases play essential roles in the processing of the viral proteins and in cleavage of host cell proteins in order to manipulate cellular processes to the advantage of the virus
This reaction was subsequently shown to be performed by the 2A proteinase (2Apro) in enteroviruses (Kräusslich et al, 1987), a chymotrypsin-like cysteine proteinase (Petersen et al, 1999), whereas in aphthoviruses, the proteolysis is performed by the leader proteinase (Lpro, illustrated in Fig. 1) (Devaney et al, 1988), a papain-like cysteine proteinase (Guarné et al, 1998)
Cleavage of the eIF4G homologues prevents recruitment of capped mRNAs to the ribosome (Lamphear et al, 1995) whereas viral RNA can still be translated under these conditions as it initiates via an internal ribosome entry segment (IRES) (Martinez-Salas and Ryan, 2010)
Summary
Encoded proteinases play essential roles in the processing of the viral proteins and in cleavage of host cell proteins in order to manipulate cellular processes to the advantage of the virus. One of the first such reactions to be documented was the modification of cellular translation factors during picornaviral replication leading to the shut-off of protein synthesis from capped cellular mRNA (Etchison et al, 1982; Leibowitz and Penman, 1971) This reaction was subsequently shown to be performed by the 2A proteinase (2Apro) in enteroviruses (Kräusslich et al, 1987), a chymotrypsin-like cysteine proteinase (Petersen et al, 1999), whereas in aphthoviruses, the proteolysis is performed by the leader proteinase (Lpro, illustrated in Fig. 1) (Devaney et al, 1988), a papain-like cysteine proteinase (Guarné et al, 1998). Lpro has been shown to be involved in impairing the host innate immune defence by influencing NF-κB activation and to have deubiquitinase activity (de Los Santos et al, 2007, 2009; Skern and Steinberger, 2014)
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