The active center of human glutaredoxin(hGrx1)shares a common thioredoxin fold and specific affinity for substrate glutathione (GSH)with natural glutathione peroxidase(GPx).hGrx1 was redesigned to introduce the catalytic selenocysteine residue to imi- tate the function of antioxidant selenoenzyme GPx in vivo.The human hGrx1 scaffold is a good candidate for potential medical application compared with other animal-originated protein scaffolds.Two consecutive rare codons(AGG-AGG)in the open reading frame of hGrx1 mRNA encoding Arg26-Arg27 residues can reduce seleno-hGrx1 expression level significantly in the Cys auxotrophic Escherichia coli strain BL21cysE51.Therefore,we optimized the rare codons,which resulted in a remarkable in- crease of the expression level in the Cys auxotrophic cells,which may be sufficient for future medical production.The engineered artificial selenoenzyme displays high GPx catalytic activity,rivaling that of some natural GPx proteins.Kinetic analysis of the engineered seleno-hGrx1 showed a typical ping-pong kinetic mechanism;its catalytic properties are similar to those of some nat- urally occurring GPx proteins.
Glutathione peroxidase (GPx) is a vital antioxidant enzyme involved in the reduction of reactive oxygen species and protects cells from oxidative damage.Consequently enormous efforts have been devoted to developing artificial catalysts with GPx function.Besides the research on enhancing the catalytic activity of GPx mimics,the design and construction of smart GPx models has also inspired great interest.Herein,a novel photo-responsive seleniumcontaining vesicular GPx model was successfully constructed by supramolecular self-assembly of the cationic surfactant PyC10AZoC10Py with benzeneseleninic acid (PhSeO2H) through hydrophobic and electrostatic interactions in aqueous media.This selenium-containing vesicular catalyst showed remarkable GPx-like activity,which is 692times more effective than PhSeO2H for the reduction of cumene hydroperoxide (CUOOH) by 4-nitrobenzenethiol (NBT).Interestingly,when an equimolar amount of α-CD was added,the GPx-like activity of the catalytic vesicle declines remarkably due to the vesicle disaggregation in the presence ofα-CD.Whereas the biomimetic system was irradiated by UV light at 365 nm,the catalytic vesicle was formed again and the GPx-like activity recovered.
Ruiqing XiaoLipeng ZhouZeyuan DongYuzhou GaoJunqiu Liu
Enzymes are biomacromolecules responsible for the abundant chemical biotransformations that sustain life. Recently, biochemists have discovered that multiple conformations and numerous parallel paths are involved during the processes catalyzed by enzymes. It is plausible that the entire macromolecular scaffold is involved in catalysis via cooperative motions that result in incredible catalytic efficiency. Moreover, some enzymes can very strongly bind the transition state with an association constant of up to 1024 M-1, suggesting that covalent bond formation is a possible process during the conversion of the transition state in enzyme catalysis, in addition to the concatenation of noncovalent interactions. Supramolecular chemistry provides fundamental knowledge about the relationships between the dynamic structures and functions of organized molecules. By tak-ing advantage of supramolecular concepts, numerous supramolecular enzyme mimics with complex and hierarchical structures have been designed and investigated. Through the study of supramolecular enzyme models, a great deal of information to aid our understanding of the mechanism of catalysis by natural enzymes has been acquired. With the development of supramolec-ular artificial enzymes, it is possible to replicate the features of natural enzymes with regards to their constitutional complexity and cooperative motions, and eventually decipher the conformation-based catalytic mystery of natural enzymes.
