Chemically engineered papain as artificial formate dehydrogenase for NAD(P)H regeneration

Abstract

Organometallic complexes of the general formula [(η⁶-arene)Ru(N⁁N)Cl]⁺ and [(η⁵-Cp*)Rh(N⁁N)Cl]⁺ where N⁁N is a 2,2′-dipyridylamine (DPA) derivative carrying a thiol-targeted maleimide group, 2,2′-bispyridyl (bpy), 1,10-phenanthroline (phen) or ethylenediamine (en) and arene is benzene, 2-chloro-N-[2-(phenyl)ethyl]acetamide or p-cymene were identified as catalysts for the stereoselective reduction of the enzyme cofactors NAD(P)⁺ into NAD(P)H with formate as a hydride donor. A thorough comparison of their effectiveness towards NAD⁺ (expressed as TOF) revealed that the Rh^III complexes were much more potent catalysts than the Ru^II complexes. Within the Ru^II complex series, both the N⁁N and arene ligands forming the coordination sphere had a noticeable influence on the activity of the complexes. Covalent anchoring of the maleimide-functionalized Ru^II and Rh^III complexes to the cysteine endoproteinase papain yielded hybrid metalloproteins, some of them displaying formate dehydrogenase activity with potentially interesting kinetic parameters.