Emulating functions of natural enzymes in man-made constructs has proven challenging. Here we describe a man-made protein platform that reproduces many of the diverse functions of natural oxidoreductases without importing the complex and obscure interactions common to natural proteins. Our design is founded on an elementary, structurally stable 4-α-helix protein monomer with a minimalist interior malleable enough to accommodate various light- and redox-active cofactors and with an exterior tolerating extensive charge patterning for modulation of redox cofactor potentials and environmental interactions. Despite its modest size, the construct offers several independent domains for functional engineering that targets diverse natural activities, including dioxygen binding and superoxide and peroxide generation, interprotein electron transfer to natural cytochrome c and light-activated intraprotein energy transfer and charge separation approximating the core reactions of photosynthesis, cryptochrome and photolyase. The highly stable, readily expressible and biocompatible characteristics of these open-ended designs promise development of practical in vitro and in vivo applications.

Potassium periodate (PI, KIO 4 ) was readily activated by Fe(II) under acidic conditions, resulting in the enhanced abatement of organic contaminants in 2 min, with the decay ratios of the selected pollutants even outnumbered those in the Fe(II)/ peroxymonosulfate and Fe(II)/peroxydisulfate processes under identical conditions. Both 18 O isotope labeling techniques using methyl phenyl sulfoxide (PMSO) as the substrate and Xray absorption near-edge structure spectroscopy provided conclusive evidences for the generation of high-valent iron−oxo species (Fe(IV)) in the Fe(II)/PI process. Density functional theory calculations determined that the reaction of Fe(II) with PI followed the formation of a hydrogen bonding complex between Fe(H 2 O) 62+ and IO 4 (H 2 O) − , ligand exchange, and oxygen atom transfer, consequently generating Fe(IV) species. More interestingly, the unexpected detection of 18 O-labeled hydroxylated PMSO not only favored the simultaneous generation of • OH but also demonstrated that • OH was indirectly produced through the self-decay of Fe(IV) to form H 2 O 2 and the subsequent Fenton reaction. In addition, IO 4− was not transformed into the undesired iodine species (i.e., HOI, I 2 , and I 3 − ) but was converted to nontoxic iodate (IO 3 − ). This study proposed an efficient and environmental friendly process for the rapid removal of emerging contaminants and enriched the understandings on the evolution mechanism of • OH in Fe(IV)-mediated processes.

The study of natural enzymes is complicated by the fact that only the most recent evolutionary progression can be observed. In particular, natural oxidoreductases stand out as profoundly complex proteins in which the molecular roots of function, structure and biological integration are collectively intertwined and individually obscured. In the present paper, we describe our experimental approach that removes many of these often bewildering complexities to identify in simple terms the necessary and sufficient requirements for oxidoreductase function. Ours is a synthetic biology approach that focuses on from-scratch construction of protein maquettes designed principally to promote or suppress biologically relevant oxidations and reductions. The approach avoids mimicry and divorces the commonly made and almost certainly false ascription of atomistically detailed functionally unique roles to a particular protein primary sequence, to gain a new freedom to explore protein-based enzyme function. Maquette design and construction methods make use of iterative steps, retraceable when necessary, to successfully develop a protein family of sturdy and versatile single-chain three- and four-α-helical structural platforms readily expressible in bacteria. Internally, they prove malleable enough to incorporate in prescribed positions most natural redox cofactors and many more simplified synthetic analogues. External polarity, charge-patterning and chemical linkers direct maquettes to functional assembly in membranes, on nanostructured titania, and to organize on selected planar surfaces and materials. These protein maquettes engage in light harvesting and energy transfer, in photochemical charge separation and electron transfer, in stable dioxygen binding and in simple oxidative chemistry that is the basis of multi-electron oxidative and reductive catalysis.