Designing ligands for tuning the active site of novel artificial vanadium-based enzymes for sulfoxidation.

Artificial metalloenzymes, which are formed by inserting inorganic complexes into biological scaffolds, have attracted interest as a potential biotechnological alternative of natural enzymes. In this study, vanadium complexes were incorporated as artificial active sites for sulfoxidation catalysis within NikA, a bacterial Ni(II) import protein. Two of the designed metal complexes, namely VOL1 and VOL3, which are based on either an amino alcohol or an amino acid ligand, respectively, were spectroscopically and structurally characterized, demonstrating transformation of a VOL3 into a VO(L3)2 species. This study has highlighted the capacity of NikA to bind inorganic complexes at different sites. Unlike VOL3, VO(L3)2 complex is stabilized within the well-characterized natural binding site. Conversely, the planar structure of VOL1 prevents similar binding, instead allowing a novel binding mode within the protein. VOLX@NikA-based cross-linked enzyme crystals were then used as catalysts for sulfide oxidation. This work highlights the versatility of the NikA protein in binding inorganic complexes, as well as the different reactivities of VOLX-based cross-linked enzyme crystals (CLEC) in catalyzing oxidation reactions.