The Construction Of Dendrimer-based Self-assembling Protein Nanomaterials

As the most important biomacromolecules in living organisms, proteins are involved in almost all biological activities in molecular levels. Scientists have focused their research interests on protein self-assembly, not only for disclosing protein-protein interactions, but also for designing advanced bionanomaterials, such as diagnosis and treatment of diseases, artificial tissues, and biomachines. We also noticed that the explosive researches have been made in designing the functional protein nanomaterials, but there are still some scientific domains need to be expanded and enriched. It is the most important means for chemically-triggerred protein self-assembly to design the protein nanomaterials, such as metal-mediated interaction, electrostatic interaction, molecular specific recognition, and convalent interaction. Furthermore, these protein nanomaterials are also used to design the nanoenzyme mimics, artificial light-harvesting systems, smart drug release and nanoreactors.Dendrimers are usually called as the “artificial proteins” for their distinctive molecular components and perfect three dimensional(3D) architectures. The design of dendrimer porphyrins is inspired by the unique structures of hemoproteins, and can be used to study the biofunction and catalytic mechanism in vitro. In addition, their fundamental properties have led to the commercial use of dendrimers as globular protein replacements for immunodiagnostics and in vitro gene expression applications. In fact, it shouldn’t be the end of the “artificial protein” investigation for the dendrimers. They would be the perfect candidates for the investigation of protein interactions, for the design of protein nanomaterials, and for the treatment of protein-related diseases. We also hope we can provide a new train of thought for the design of protein nanomaterials by investigating the dendrimer self-assembly behaviors and the dendrimer-mediated protein self-assembly.1. In Situ Self-Adjusting Assembly of Ill-Defined PAMAM DendrimerAs most of native proteins, there are a lot of amino groups around the surface of PAMAM dendrimers, so they exhibit some protein-like structures and properties. In this chapter, we try to disclose the protein self-assembling behaviors by investigating the small molecule mediated amphiphilic assembly of dendrimers. Benzaldehyde can in situ interact with amino groups of the first generation PAMAM(PD1) dendrimer to form dynamic covalent bond, the schiff base bond. The partially decorated PD1 dendrimer with ill-defined structure can self-adjust to afford amphiphilic structure in the PBS buffer, and the hydrophobic domains will aggregate together to form long nanofibrils. These nanofibrils can further second assembly to nanofibers or giant microwires. In addition, the morphology of the assemblies can be affected by the acid-base properties of the solution. The Schiff-base bands will be hydrolyzd when decrease the p H value, which causing the structures disassembled. Also after exposing to the air, the morphology of assemblies can transform from fibers to globular micelles. The self-assembly of in situ decorated dendrimer is meaningful for investigating the protein amphiphilic assembly.2. Self-Assembling SP1 Protein Nanowires Mediated by PAMAM DendrimerPAMAM dendrimers are usually used as globular proteins to investigate protein-protein and protein-DNA interactions. This chapter will be focused the research interests on how to direct the protein self-assembly with dendrimers. The surface analysis shows that there is an electronegative cavity on each surface of SP1 cricoid protein, while positive charges are mainly foused on the inside and outside surfaces. We think that positive nanoparticles with comparable size may electrostatically interact with proteins, causing the protein arranged face to face to form one dimensional protein nanoarrays. Herein, we employ an “artificial globular protein”, the fifth generation PAMAM(PD5) dendrimer, to electrostatically induce protein self-assembly. We found globular PD5 can interact with top/bottom surfaces of SP1, and a giant “globular protein” can interact with two proteins in the opposite direction to form “sandwich” structure, further leading to linear protein nanowires. Furthermore, it is the multiple electrostatic interactions between SP1 and PD5 that makes the protein nanowires stable under certain ionic strength, p H value, temperature and buffer.3. Construction of Dual-Enzyme Cooperative Antioxidative Protein NanowiresHighly-ordered protein nanoarrays are usually used by scientists to design the advanced functional protein-based nanomaterials. The dendrimer-protein binary assembly system is very helpful for the investigation of the multi-functions cooperation mechanism in organism and for the design of the multi-functions intergrated nanobiomaterials. In this chapter, we want to develop a dual-enzyme cooperative catalytic system based on the PD5 induced SP1 nanowires, and investigate the complex biocatalysis progress in organism. We select an ideal position on SP1 for site-directed mutanting of selenocysteine to design Se SP1 with glutathione peroxidase(GPx) activity. On the other hand, the amino groups around the PD5 dendrimer can convalently interact with superoxide dismutase(SOD) mimics. Thus, we found that it is not only affords the original assembling structure for dendrimer mediated protein self-assemblies, but also realizes the construction of nanoenzymes with dual-enzyme cooperation and intergrated catalytic sites. Furthermore, the developed dual-enzyme cooperative system exhibits both excellent GPx and SOD activities, and can protect the mitochondria from being damaged by reactive oxygen species(ROS). Also, the system exhibits good biocompatibility, excellent cell uptake behaviors and ultralow cell toxicity.4. The Design of Photocontrolled Reversible Protein NanowiresRecent years, protein nanomaterials are gradually developing from “structuralization” to“intelligence”. Scientists are already able to develop all kinds of protein nanostructures by accurately controlling the protein-protein interacting behaviors. But it is still full of challenge how to switch the assembling morphologies by dynamically controlling the protein-protein interactions. Herein, light-activable allosteric PAMAM dendrimer is employed to control the protein assembly behaviors. Light can be used to reversibly switching the configuration of the fourth generation azobenzene-cored PAMAM dendrimer(Azo PD4) between trans-form and cis-form, further causing the protein assembly morphologies changed. We found Azo PD4 can manipulate the SP1 proteins into parallel arrangement along its C6 symmetry axis by face to face to form straight nanowires under visible light. However, when it is isomerized to cis-form under UV light(365 nm) irradiation, it could manipulate the SP1 rings aligning with a certain interspace angle, making the protein nanowires bending to curve structures. Furthermore, the protein nanowires could be reversibly interconverted by alternatively irradiating under visible light and UV light. Crucially, light can be used to control the curvature of the assemblies through the photocontrolled reversible morphology conversion of the protein nanowires.