Hydrogen production by a fully de novo enzyme

Abstract

Molecular catalysts based on abundant elements that function in neutral water represent an essential component of sustainable hydrogen production. Artificial hydrogenases based on protein-inorganic hybrids have emerged as an intriguing class of catalysts for this purpose. We have prepared a novel artificial hydrogenase based on cobaloxime bound to a de novo three alpha-helical protein, α3C, via a pyridyl-based unnatural amino acid. The functionalized de novo protein was characterized by UV-visible, CD, and EPR spectroscopy, as well as MALDI spectrometry, which confirmed the presence and ligation of cobaloxime to the protein. The new de novo protein produced hydrogen under electrochemical, photochemical and reductive chemical conditions in neutral water solution. A change in hydrogen evolution capability of the de novo enzyme compared with native cobaloxime was observed, with tunover numbers around 80% for that of cobaloxime, and hydrogen evolution rates of 40% of that of cobaloxime. We discuss these findings in the context of existing literature, and our study contributes important information about the functionality of cobaloxime HER catalysts in protein environments, and the feasibility of artificial enzymes to the field of artificial metalloenzymes. Small de novo proteins as enzyme scaffolds have the potential to function as upscaleable bioinspired catalysts thanks to their efficient atom economy, and the findings presented here show that this type of novel enzymes are a possible product.