Construction Of Supramolecular Bifunctional Enzyme Model With SOD And GPx Activities

The antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) contribute dominatingly to enhance cellular antioxidative defense against oxidative stress in the human body. Thereinto, SOD is a metalloenzyme that catalyzes the dismutation of superoxide radical anion (O2-·)to H2O2 and dioxygen. H2O2 is then detoxified either to H2O and O2 by catalase (CAT) or to H2O by glutathione peroxidase (GPx) (Scheme 1). Studies indicated that each enzyme has a specific as well as an irreplaceable function and they act in a cooperative or synergistic way to ensure a global cell protection, and only when an appropriate balance between the activities of these enzymes is maintained, the optimal protection of cells could be achieved.In recent years, there were considerable interests in preparing the enzyme mimics with the properties of SOD or GPx for elucidating catalytic mechanism and for potential pharmaceutical application. In order to further study the cooperation of these enzymes in antioxidation and to generate efficient therapeutic agents, some bifunctional artificial enzymes with antioxidant enzyme activities have been constructed by chemical methods. However, successful construction of a bifunctional enzyme which has both SOD and GPx activities by using a supramolecular method remains a challenge. Furthermore, for the bifunctional enzyme models with high catalytic activity, how to modulate the activity is another goal that we are pursing.Recent years, the development in supramolecular and nano science brings a new field in the design of artificial enzyme. Herein, based on the understanding of the cooperative or synergistic way between natural antioxidant enzymes, utilizing a'supramolecular linker'which constructed through the host-guest interaction between adamantane andβ-cyclodextrin, a simple bifunctional artificial enzyme with a porphyrin core and four cyclodextrin-based suspensory tellurol moieties has been designed and prepared. The Mn(Ⅲ) porphyrin acted as an efficient active site of SOD, and tellurol moiety endowed GPx activity. Compared with other bifunctional antioxidative enzyme mimics, this supramolecular artificial enzyme has its obvious advantage: simple preparation process and remarkable catalytic activity. Furthermore, in order to better design a bifunctional enzyme model in which the catalytic center and binding site were well matched, a supramolecular hyperbranched polymer bifunctional enzyme model was constructed by supramolecular self-assembly. As anticipated, the model demonstrated high SOD and GPx catalytic activity. Finally, a smart star-shaped pseudo-block copolymer catalyst with both SOD and GPx activities was constructed by the self-assembly of a porphyrin core with four suspensory adamantyl moieties andβ-cyclodextrin-terminated temperature-sensitive copolymer through host-guest interaction in aqueous solution. With the change of the temperature, it exhibits stable SOD-like activity and high GPx catalytic efficiency with temperature dependence characteristic.1. Simple bifunctional artificial enzymeIn order to further study the cooperation of these enzymes in antioxidation and to generate efficient therapeutic agents, bifunctional enzymes with both SOD and GPx activities have been constructed by chemical methods in our group and others. However, successful construction of a bifunctional enzyme which has both SOD and GPx activities by using a supramolecular method remains a challenge. Herein, utilizing a'supramolecular linker'which constructed through the host-guest interaction between adamantane andβ-cyclodextrin, a bifunctional artificial enzyme with a porphyrin core and four cyclodextrin-based suspensory tellurol moieties has been designed and prepared. The Mn(Ⅲ) porphyrin acted as an efficient active site of SOD, and tellurol moiety endowed GPx activity. The SOD-like activity (IC50) of the new catalyst was found to be 0.116μM and equals to 2.56% of the activity of the native SOD. Besides this, supramolecular enzyme model also showed a high GPx activity, and a remarkable rate enhancement of 27-fold compared to the well-known GPx mimic ebselen was observed. More importantly the supramolecular artificial enzyme showed good thermal stability. Compared with other bifunctional antioxidative enzyme mimics, this supramolecular artificial enzyme has its obvious advantage: simple preparation process and remarkable catalytic activity.2. Supramolecular hyperbranched polymer as bifunctional enzyme modelIn order to better design a bifunctional enzyme model in which the catalytic center and binding site were well matched, and demonstrate high catalytic activity, a supramolecular hyperbranched polymer enzyme model with MnTPyP-M-Ad and 6-Te-diCD was constructed by supramolecular self-assembly. The formation of the expected structure was proved by NMR, SEM, Malvern-ZetaSizer Nano ZS, etc. The experiment confirmed that the GPx-like activity increased 1.4-fold than 6-Te-diCD in which cavities were occupied by adamantane carboxylic. Utilizing this supramolecuar strategy to construct GPx mimic, considering the simple procedure and easy modulation, it is supposed to provide a new method to construct antioxidative enzyme model.3. Modulatory bifunctional artificial enzyme with temperature responsive catalytic activityUnder normal conditions, ROS are friendly for us and play a role as vital signal molecules in metabolism, and they will not result in various illnesses unless they are overproduced in the human body. In order to realize the modulation of the catalytic activity and also the double control of the function of ROS, we present a novel smart bifunctional enzyme model with both SOD and GPx activities comprising a temperature-sensitive block copolymer (β-CD-PEG-b-PNIPAAm-Te) which can self-assembly with MnTPyP-M-Ad through host-guest complexation for the first time. We measured the optical transparences of pure copolymer and pseudo-block copolymer in aqueous medium, and cofirmed that the LCSTs are 33.8 and 35.6°C respectively, which are higher than the pure PNIPAAm homopolymer. It seems that the elevated LCST is attributed to the metamorphic head-group effect. To investigate the temperature responsive property of the enzyme models, the SOD and GPx activities were determined in the different system against temperature respectively. The mimic exhibited stable SOD-like activity and high GPx catalytic efficiency with temperature-responsive dependence characteristic. Furthermore, by adjusting LCST through assembling with a"supramolecular-linker", this smart enzyme model exhibited the highest GPx catalytic efficiency in close to body temperature (37°C). The experiment confirmed that the adjustment and control of LCST of these materials play an important role in modulating the catalytic activity.