Foot-and-mouth disease virus leader proteinase: Structural insights into the mechanism of intermolecular cleavage

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.