Probing the Surface of a Laccase for Clues towards the Design of Chemo-Enzymatic Catalysts

Abstract

Systems featuring a multi-copper oxidase associated with transition-metal complexes can be used to perform oxidation reactions in mild conditions. Here, a strategy is presented for achieving a controlled orientation of a ruthenium-polypyridyl graft at the surface of a fungal laccase. Laccase variants are engineered with unique surface-accessible lysine residues. Distinct ruthenium-polypyridyl-modified laccases are obtained by the reductive alkylation of lysine residues precisely located relative to the T1 copper centre of the enzyme. In none of these hybrids does the presence of the graft compromise the catalytic efficiency of the enzyme on the substrate 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid). Furthermore, the efficiency of the hybrids in olefin oxidation coupled to the light-driven reduction of O₂ is highly dependent on the location of the graft at the enzyme surface. Simulated Ru^II -Cu^II electron coupling values and distances fit well the observed reactivity and could be used to guide future hybrid designs.

Keywords: electron transfer; enzyme models; multi-copper oxidase surfaces; photosensitisers; targeted functionalisation.