Natural enzymes are remarkable molecular machines that enable all sorts of essential biochemical reactions. For decades, scientists have sought to create artificial versions of these catalysts for industrial and biomedical applications. However, they have struggled to match nature’s efficiency and simplicity. This, in turn, has hindered the development of environmentally friendly catalysts for sustainable chemistry.

Creating artificial enzymes typically requires either cofactors or complex structural arrangements that precisely position reactive groups in three-dimensional space. These requirements constrain design flexibility, often resulting in enzymes that underperform compared to their natural counterparts. Finding simpler approaches that don’t sacrifice catalytic power has remained an elusive goal in the field of biocatalysis.

Against this backdrop, a research team led by Professor Takafumi Ueno from the Institute of Science Tokyo, Japan, reported a novel approach to enzyme design using protein nanocages. Their paper, published in Angewandte Chemie on April 24, 2025, demonstrates how precisely arranged histidine amino acids inside a ferritin protein cage can function as a highly effective metal-free peroxidase—an enzyme that drives oxidation reactions using hydrogen peroxide as a reactant.

The researchers engineered the ferritin cage by introducing histidine residues and a series of targeted mutations. By taking advantage of ferritin’s ability to self-assemble into protein cages, they created clusters of histidine residues on the cage’s inner surface. These histidine clusters act as catalytic centers, mimicking peroxidase activity that promotes reactions between hydrogen peroxide and 3,3′, 5,5′-tetramethylbenzidine substrate.

“The engineered ferritin variant showed approximately 80 times higher reaction efficiency compared to conventional oligohistidine assemblies,” remarks Prof. Ueno.

The team’s innovative approach demonstrates that the proper spatial arrangement of simple amino acids can eliminate the need for metal cofactors in certain enzymatic reactions. Through careful positioning of these amino acids at the interfaces of the ferritin cage, the team produced a confined reaction environment that significantly enhanced catalytic activity.

Using molecular dynamics simulations, they revealed how the ferritin cage confines reactants in close proximity to the histidine clusters, explaining the dramatic enhancement in catalytic efficiency.

“Based on theoretical calculations, we confirmed that this high activity is further enhanced by a ‘confined environment effect’ within the protein cage, which concentrates reactants and facilitates their interaction,” says Prof. Ueno.

These exciting findings unlock new possibilities for protein cages in metal-free catalytic systems, which could find applications in sustainable chemical production, biomaterials development, and environmental remediation. “This research represents a major advancement in artificial enzyme design and environmentally friendly catalysis, paving the way for the development of sustainable biocatalysts,” concludes Prof. Ueno.

In the near future, further studies in this field could lead to high-performance bioinspired catalysts. By refining the spatial design of catalytic residues and exploring other self-assembling protein frameworks, researchers may develop a broader range of metal-free enzymes tailored for specific industrial or biomedical tasks.

Such advances would not only improve catalytic efficiency but also reduce reliance on rare or toxic metals, making green chemistry more accessible and practical for real-world applications across various sectors.