Katalyse und Elektronentransfer in helikalen De‐novo‐Gerüststrukturen

Design of Artificial Enzymes: Insights into Protein Scaffolds

The design of artificial enzymes has emerged as a promising tool for the generation of potent biocatalysts able to promote new-to-nature reactions with improved catalytic performances, providing a powerful platform for wide-ranging applications and a better understanding of protein functions and structures. The selection of an appropriate protein scaffold plays a key role in the design process. This review aims to give a general overview of the most common protein scaffolds that can be exploited for the generation of artificial enzymes. Several examples are discussed and categorized according to the strategy used for the design of the artificial biocatalyst, namely the functionalization of natural enzymes, the creation of a new catalytic site in a protein scaffold bearing a wide hydrophobic pocket and de novo protein design. The review is concluded by a comparison of these different methods and by our perspective on the topic.

The pH-Induced Selectivity Between Cysteine or Histidine Coordinated Heme in an Artificial α-Helical Metalloprotein

De Novo metalloprotein design assesses the relationship between metal active site architecture and catalytic reactivity. Herein, we use an α-helical scaffold to control the iron coordination geometry when a heme cofactor is allowed to bind to either histidine or cysteine ligands, within a single artificial protein. Consequently, we uncovered a reversible pH-induced switch of the heme axial ligation within this simplified scaffold. Characterization of the specific heme coordination modes was done by using UV/Vis and Electron Paramagnetic Resonance spectroscopies. The penta- or hexa-coordinate thiolate heme (9≤pH≤11) and the penta-coordinate imidazole heme (6≤pH≤8.5) reproduces well the heme ligation in chloroperoxidases or cyt P450 monooxygenases and peroxidases, respectively. The stability of heme coordination upon ferric/ferrous redox cycling is a crucial property of the construct. At basic pHs, the thiolate mini-heme protein can catalyze O₂ reduction when adsorbed onto a pyrolytic graphite electrode.

Making or Breaking Metal-Dependent Catalytic Activity: The Role of Stammers in Designed Three-Stranded Coiled Coils

While many life-critical reactions would be infeasibly slow without metal cofactors, a detailed understanding of how protein structure can influence catalytic activity remains elusive. Using de novo designed three-stranded coiled coils (TRI and Grand peptides formed using a heptad repeat approach), we examine how the insertion of a three residue discontinuity, known as a stammer insert, directly adjacent to a (His)3 metal binding site alters catalytic activity. The stammer, which locally alters the twist of the helix, significantly increases copper-catalyzed nitrite reductase activity (CuNiR). In contrast, the well-established zinc-catalyzed carbonic anhydrase activity (p-nitrophenyl acetate, pNPA) is effectively ablated. This study illustrates how the perturbation of the protein sequence using non-coordinating and non-acid base residues in the helical core can perturb metalloenzyme activity through the simple expedient of modifying the helical pitch adjacent to the catalytic center.