Tiezheng Pan

Reversible Ca2+ Switch of An Engineered Allosteric Antioxidant Selenoenzyme†

A Ca(2+) -responsive artificial selenoenzyme was constructed by computational design and engineering of recoverin with the active center of glutathione peroxidase (GPx). By combining the recognition capacity for the glutathione (GSH) substrate and the steric orientation of the catalytic selenium moiety, the engineered selenium-containing recoverin exhibits high GPx activity for the catalyzed reduction of H2 O2 by glutathione (GSH). Moreover, the engineered selenoenzyme can be switched on/off by Ca(2+) -induced allosterism of the protein recoverin. This artificial selenoenzyme also displays excellent antioxidant ability when it was evaluated using a mitochondrial oxidative damage model, showing great potential for controlled catalysis in biomedical applications.

Enzyme-Triggered Defined Protein Nanoarrays: Efficient Light-Harvesting Systems to Mimic Chloroplasts

The elegance and efficiency by which chloroplasts harvest solar energy and conduct energy transfer have been a source of inspiration for chemists to mimic such process. However, precise manipulation to obtain orderly arranged antenna chromophores in constructing artificial chloroplast mimics was a great challenge, especially from the structural similarity and bioaffinity standpoints. Here we reported a design strategy that combined covalent and noncovalent interactions to prepare a protein-based light-harvesting system to mimic chloroplasts. Cricoid stable protein one (SP1) was utilized as a building block model. Under enzyme-triggered covalent protein assembly, mutant SP1 with tyrosine (Tyr) residues at the designated sites can couple together to form nanostructures. Through controlling the Tyr sites on the protein surface, we can manipulate the assembly orientation to respectively generate 1D nanotubes and 2D nanosheets. The excellent stability endowed the self-assembled protein architectures with promising applications. We further integrated quantum dots (QDs) possessing optical and electronic properties with the 2D nanosheets to fabricate chloroplast mimics. By attaching different sized QDs as donor and acceptor chromophores to the negatively charged surface of SP1-based protein nanosheets via electrostatic interactions, we successfully developed an artificial light-harvesting system. The assembled protein nanosheets structurally resembled the natural thylakoids, and the QDs can achieve pronounced FRET phenomenon just like the chlorophylls. Therefore, the coassembled system was meaningful to explore the photosynthetic process in vitro, as it was designed to mimic the natural chloroplast.

CHAPTER 33:Selenium and Antioxidant Microgels

Selenium is a dietary-essential trace element and plays a vital role in human health. Its major biological function is to participate in the construction of the active center of selenoenzymes that serve as antioxidants to regulate the reactive oxygen species level within the cell. Selenium deficiency is associated with a variety of human diseases because a low-selenium status will cause excessive reactive oxygen species to damage the cellular components and induce an intracellular oxidative stress. Recently, the development of artificial antioxidants as a new source to replace natural selenoenzymes has attracted increasing interest for biomedical applications. To date, various strategies including chemical and biological methods have been proposed to design selenoenzyme mimics on different scaffolds, ranging from synthetic compounds to self-assembled composites, based on the mechanism and structure of the well-studied selenoenzyme, glutathione peroxidase. In this chapter, we will focus on the introduction of microgels as a new class of platform to design artificial selenoenzymes and also provide two examples of how to construct advanced antioxidant microgels for intelligent or synergistic catalysis through utilizing their inherent advantages such as water solubility, biocompatibility, multicomponents, and environmental responsiveness.