Design,Synthesise And Applications Of Functional Self-Assembling Peptide Nanomaterials

Peptides with low molecular weight are easier to be synthesized and modified compared with proteins.Therefore,peptides can be designed,synthesized and assembled into precisely controllable molecular structures,further interacting formation of nanostructures.Self-assembling peptide nanomaterials have many advantages compared with conventional polymer materials,such as stability,responsibility,cell selectivity and so on.The biomaterials can be constructed using self-assembling peptides with good bioactivities and functions,which has important guidance for the development of new biomaterials.However,though the exploration of biomaterials has a good progress,there are still shortages of a systematic understanding on the design,mechanism of self-assembling and relationship between structures and functions of peptides.This thesis focused on the functional self-assembling peptide nanomaterials and studied the self-assembling mechanism and applications for drug delivery.The accomplishments are summarized as follows:1.Design,synthesis and self-assembling mechanism of chimeric peptide assembly.The sequences were optimized using two types of peptides——coiled coil and collagen mimetic peptides as templates to obtain a new coiled coil peptide,26r(EALKWEIEALKCEIEALKAEIEALKA),and two new collagen mimetic peptides,P6(PCGPOGPOGPOGPOGPOGPOG)and P7(PCGPOGPOGPOGPOGPOGPOG).26 r was conjugated with P6 and P7 through a disulfide bond,respectively.Two chimeric peptides P6-26 r and P7-26 r were successfully constructed.Both two chimeric peptides could self-assemble to hexameric structures.P7-26 r hexamer has more stable structures than P6-26 r.It was proved that the chimeric peptides mainly formed into hexamers at high concentrations.As the concentration decreased,a small amount of trimers occurred and there existed an equilibrium between hexamers and trimers.Further studies showed that the hexamers were not regular spheres.Six chimeric peptide monomers were bonded together through three coiled coil dimers and two collagen triple helixes to form a trigonal bipyramidal-like hexameric nanostructure.Each domain remained its original conformation in the stable state.2.Self-assembling mechanism and applications of chimeric peptides with multivalent ligands.The sequence was further optimized using collagen mimetic peptide as a template and a short peptide RGDS was introduced as a targeting ligand.Another new collagen mimetic peptide with a targeting ligand,RGDS-P7(RGDSGGPOGPOGPOGPOGPOGPOGPOGPCG)was then obtained.It was then conjugated with 26 r by a disulfide bond and a new chimeric peptide contained a targeting ligand,named(RGDS-P7)-26 r,was constructed.(RGDS-P7)-26 r was also proved to self-assembled to a hexamer.The state and structure of(RGDS-P7)-26 r were not affected after introducing the ligand.(RGDS-P7)-26 r hexamer had a lower cytotoxicity.Several different chimeric peptides with local targeting ligand forming to dimers and trimers were synthesized subsequently,as well as a chimeric peptide without a ligand and with a scrambled ligand.Tumor targeting efficiency was studied on these chimeric peptides.The results showed that the tumor targeting efficiency of hexamers with targeting ligand RGDS was much higher than that of dimers,trimers or hexamers with scrambled ligand and without ligand.It has confirmed that tumor targeting could be achieved only when the hexameric structure and specific ligand exited simultaneously.3.Design and applications of amphiphilic cationic branched peptides.Three amphiphilic cationic branched peptides,FH-K6(bis(FHFHFH)-K-K6),FL-K6(bis(FLFHFHFH)-K-K6)and FFL-K6(bis(FFLFFHHH)-K-K6)were designed from the cell-penetrating peptide,K6.They all self-assembled to nano-vesicles through hydrophobic interaction.Plasmid DNA combined with peptide nano-vesicles through electrostatic interaction to form peptide/p DNA complexes.Three branched peptides could completely compact with p DNA at low N/P ratios,and FFL-K6 had the highest compression capability.These three peptides and their complexes with p DNA had low cytotoxicity,which suggested that they had good biocompatibility.FFL-K6 had the lowest cytotoxicity.Meanwhile,the gene transfection efficiency of three peptides was higher than the positive control,PEI-25 K.FFL-K6 had the highest transfection efficiency at N/P=10,which has broad application prospects as a non-viral vector in gene delivery and extends the application of peptide assemblyIn summary,we constructed a series of functional peptide self-assembling systems in this thesis.The self-assembling nanostructures with low cytotoxicity and good biocompatibility can be used to perform tumor targeting and gene delivery.They all will prove new research ideas for design and applications of self-assembling nano-materials.