Design And Study On The Self-assembly Properties Of α-helical Antimicrobial Peptides

With the development of society, cancer has become a highly deadly disease which harm to thelife and health of human, especially in developing countries. Chemotherapy and radiotherapyremain to be the main method in treating cancer. The harmful side effects and multidrug resistanceof traditional chemotherapy prompt urgent needs for novel anticancer drugs or therapeuticapproaches to overcome the defection of chemotherapy. The peptides have been the mostattractive candidate, because the properties of high affinity, target specificity, low toxicity, and lowmolecular weight. However, due to the fast excluded effect of kidney, the degradation of theenzyme, the half-life of peptide is very short, even only a few minutes. To overcome the defection,prolonging the retention time in circulation, improving the therapeutic index, people attemptedmany modification way to the peptide molecules, such as contained to liposomes, PEGylated,fatty acid or alkyl chain modified. In various modification methods, the amphiphilic polypeptide(PAs) that is the peptide covalent modified by fatty acid with monoalkyl or two alkyl chains tendto form a special molecular structure, significantly improving the stability of the polypeptidemolecule. The amphiphilic peptides tend to form nanostructure which has a hydrophobic core,consisting of hydrophobic alkyl chain, and a hydrophilic epidermis with peptide. This structurenot only can reduce the degradation of the enzyme, but also can improve the affinity to the targetsowing to the centralization of the charge, meanwhile, the special structure can decrease theexcluded of the kidney. Increasing the peptide accumulation of the cell, in other word, we canattain the desired effect with using less peptie, so we can reduce the number of injection.The previous study of Our laboratory on the α-helical peptide HPRP-A1(Ac-FKKLKKLFSKLWNWK-amide) which has fifteen amino acids, the result showed that it notonly has a strong antibacterial activity but also showed strong anticancer ability against manyhuman cancer cells with high inhibitory effect. Most of the previous studies were linked fattyacids to oligopeptide, or connect an active molecule to the fatty acid modified oligopeptide. Thisstudy is mainly on the N-terminus modification of HPRP-A1with four fatty acids with alkyl chain range from C6, C10, C14to C18, getting the four amphiphilic peptides caproic acid-HPRP-A1(PA1), capric acid-HPRP-A1(PA2), myristic acid-HPRP-A1(PA3), stearic acid-HPRP-A1(PA4).Furthermore, in order to increase the capacity of self-assembly, we synthesis the modifiedpeptide with a β-sheet sequence GGGLLLL as linker, modified with four fatty acids gettingamphiphilic peptides (C6for PA5, C10for PA6, C14for PA7, C18for PA8). On the basis, wecompared the influence of different length alkyl chain to the peptide secondary structure,antitumor activity, solubility, therapeutic index, self-assembling ability. The secondary structure ofthe peptide and the peptide analogue using the circular dichroism (CD), showing that fattyacid-modified promote the secondary structure formation. Detecting the residual amount of thepeptide at different time by the RP-HPLC, after the digestion of MMP-9at37℃, and the resultshows that the fatty acid modification can increase the stability of the amphiphilic peptide to theenzyme. When change the pH of the amphiphilic peptide solution, the solubility of the peptidesolution change, too. The peptide solution change from the solution to the suspension/emulsion,as following, the particle size also has a change. Observing by transmission electron microscope,we can see that at different pH condition, the amphiphilic peptides assemble to microspheres orfiber structure.