Kinetic and structural analysis of redox-reversible artificial imine reductases.

Three artificial imine reductases, constructed via supramolecular anchoring utilising Fe ^III -azotochelin, a natural siderophore, to bind an iridium-containing catalyst to periplasmic siderophore-binding protein (PBP) scaffolds, have previously been synthesised and subjected to catalytic testing. Despite exhibiting high homology and possessing conserved siderophore anchor coordinating residues, the three artificial metalloenzymes (ArMs) displayed significant variability in turnover frequencies (TOFs). To further understand the catalytic properties of these ArMs, their kinetic behaviour was evaluated with respect to the reduction of three cyclic imines: dihydroisoquinoline, harmaline, and papaverine. Kinetic analyses revealed that all examined ArMs adhere to Michaelis-Menten kinetics, with the most pronounced saturation profile observed for the substrate harmaline. Additionally, molecular docking studies suggested varied hydrogen-bonding interactions between substrates and residues within the artificial binding pocket. Pi-stacking and pi-cation interactions were identified for harmaline and papaverine, corroborating the higher affinity of these substrates for the ArMs in comparison to dihydroisoquinoline. Furthermore, it was demonstrated that multiple cavities are capable of accommodating substrates in close proximity to the catalytic centre, thereby rationalising the moderate enantioselectivity conferred by the unmodified scaffolds.
Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Anne-K. Duhme-Klair reports financial support was provided by Engineering and Physical Sciences Research Council. Anne-K. Duhme-Klair reports financial support was provided by Biotechnology and Biological Sciences Research Council. Alex H. Miller reports financial support was provided by Engineering and Physical Sciences Research Council. Keith S. Wilson reports financial support was provided by Engineering and Physical Sciences Research Council. Elena V Blagova reports financial support was provided by Engineering and Physical Sciences Research Council. Keith S. Wilson reports financial support was provided by Biotechnology and Biological Sciences Research Council. Guest editor for Special Issue on Artificial Metalloenzymes. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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