Construction Of Photo-responsive Supramolecular Enzyme Models With GPx Activity

Reactive oxygen species （ROS） is a series of intermediates of oxygen molecules inthe process of oxidation reaction. Under normal physiological conditions, there is adynamic balance between the generation and removal of ROS in vivo. However, inpathological conditions, or when organisms are exposed to certain external stimuli, thedynamic balance between the generation and removal of ROS will break and theirconcentration will exceed the normal physiological limits, and thus damage the biofilmand biological molecules such as DNA, proteins and carbohydrates. And eventually leadto a variety of oxidative diseases, such as atherosclerosis, myocardial infarction,hypertension, memory impairment, and even senile dementia.In the long-term evolutionary process, aiming at the oxidative damage caused byexcess ROS, organisms have established a relatively complete system of defense. GPxplays a key role in the anti-oxidation process of organism: it catalyzes GSH to clear thehydroperoxide ROOH in the body. However, due to limited sources of heterologousexpression, instability, ease to cause the shortcomings of the immune response, thedevelopment and utilization of GPx has been extremely limited. Therefore, GPx artificialsimulation has been the concern of a growing number of scientists. Using chemical andbiological principles and methods, scientists have designed and synthesized a largenumber of GPX mimics. But as they had not considered the identification of the enzymewith the substrates, the catalytic activities of these enzyme mimics were generally low.Therefore, the construction of GPx mimics with strong substrates identification ability hasbecome an important research topic.Vesicle is a class of closed layered membrane nano-assembly structure, which isspontaneously formed when amphiphilic molecules are dispersed in water. With a chargedhydrophilic surface and membrane hydrophobic core, it can include and enrich charged orhydrophobic substrates, thus speed up the rate of the reaction. Therefore, vesicle is anexcellent building skeleton for enzyme mimics. Currently, it has been widely used as nano-reactor in constructing hydrolysis catalysis, oxidation catalysis, but it has rarely beenreported as GPx enzyme model.Supramolecular Polymer is a kind of macromolecule connected from small moleculesor oligomers by complementary, reversible, directional non-covalent interactions.Compared with traditional covalent polymers, supramolecular polymers have severaldistinctive features: the diversity of the monomer; the directional reversible forcesbetween the monomers and a relatively small synthesis.Azobenzene is a typical photosensitive molecule with two isomers: the planartrans-isomer （trans） and the bent cis-isomers （cis）. In the dark or under visible light, mostof the azobenzene molecules are in the trans configuration. However, if exposed toultraviolet irradiation of specific wavelengths, azobenzene would undergo cis-to-transconfiguration change; under visible light or heat, the cis-configuration azobenzene can beback to the trans configuration. This light-induced isomerization reaction is fullyreversible with no side effects, and usually in the picosecond. Because of these advantages,azobenzene has a wide range of applications in liquid crystals, molecular machines andsmart biological materials. Since the sixties of last century, the application of theazobenzene in the regulation of enzyme activity has been developed and has become animportant methord in study the structure-function relationship of enzymes. However, theuse of light in the regulation of GPx enyme activity has rarely been reported.In recent years, our research group has successfully constructed several excellenttemperature response macromolecular GPx enzyme models. In order to broaden theapplication of intelligent control GPx enzyme mimic, we have herein designed andprepared two light responsive the supramolecular GPx enzyme models.Construction of photo-responsive vesicle GPx model: the vesicle GPx mimic isconstructed from a vesicle formed by an azobenzene-containing bola-type amphiphiliccompounds PyC10AzoC10Py and PhSeO₂H as the catalytic center. In the CUOOH-NBTactivity test system, the enzyme model shows a very high catalytic activity （50.19μMmin-1）, which is692times the catalytic activity of PhSeO₂H. We found that thesolubilization and enrichment of subtracts to the hydrophobic region of the vesicle are keyfactors for the high activity of the enzyme model. When we added some α-cyclodextrin,the vesicle deformed and the GPx catalytic activity reduced to16.50μM min-1. Then whenthe solution was exposed to UV irradiation, the vesicle re-formed and its catalytic activityrestored to40.47μM min-1. And so forth, using light to control formation and dissociationof azobenzene-α-cyclodextrin host-guest complex and the balance between hydrophilic purpose of regulating the structure and catalytic activity of the vesicle GPx enzymemodel.Construction of photo-responsive supramolecular polymer GPx model: based onthe strong identification between the cyclodextrin and adamantane, a water-solubleazobenzene-containing di-adamantane guest molecule AdAzoAd and the GPx catalyticactivity--6-TediCD were allowed to assemble into a supramolecular polymer with GPxcatalytic activity in aqueous solution. In the CUOOH-NBT activity test system, theenzyme model shows a very high catalytic activity （23.30μM min-1）, which is89.6timesthe catalytic activity of Ebselen. Containing a large number of azobenzene groups in thesupramolecular polymer main chain, we can regulate the conformation of supramolecularpolymer molecular, thus achieving the purpose of regulating GPx enzyme activity by light.We found that after illumination of365nm UV, the vitality of the enzyme model increasedto40.28μM min-1, higher than the reported6-TediCD activity.