Switching the substrate specificity of the two-component NS2B-NS3 flavivirus proteinase by structure-based mutagenesis.

The flavivirus NS2B-NS3(pro)teinase is an essential element in the proteolytic processing of the viral precursor polyprotein and therefore a potential drug target. Recently, crystal structures and substrate preferences of NS2B-NS3pro from Dengue and West Nile viruses (DV and WNV) were determined. We established that the presence of Gly-Gly at the P1'-P2' positions is optimal for cleavage by WNV NS3pro, whereas DV NS3pro tolerates well the presence of bulky residues at either P1' or P2'. Structure-based modeling suggests that Arg(76) and Pro(131)-Thr(132) limit the P1'-P2' subsites and restrict the cleavage preferences of the WNV enzyme. In turn, Leu(76) and Lys(131)-Pro(132) widen the specificity of DV NS3pro. Guided by these structural models, we expressed and purified mutant WNV NS2B-NS3pro and evaluated cleavage preferences by using positional scanning of the substrate peptides in which the P4-P1 and the P3'-P4' positions were fixed and the P1' and P2' positions were each randomized. We established that WNV R76L and P131K-T132P mutants acquired DV-like cleavage preferences, whereas T52V had no significant effect. Our work is the first instance of engineering a viral proteinase with switched cleavage preferences and should provide valuable data for the design of optimized substrates and substrate-based selective inhibitors of flaviviral proteinases.