Studies On The Effect Of Heilicity Of α-helical Peptides On Their Biological Activities

Membrane-active peptide is a class of the peptide molecules derived from the genome encoded in vivo or in vitro chemical synthesis, which can defend the exogenous malignant factors against the host and recognize the diseased cells and removed it specifically. Membrane-active peptides are short and small peptide molecules which is composed of 12-100 amino acids generally. Currently, membrane-active peptides have become a global research focus, especially due to their broad-spectrum antimicrobial activity, including Gram-negative bacteria, Gram-positive bacteria and fungi, and its strong killing capacity on the tumor cell specifically (specificity is that they can not only kill cancer cells, but also have no toxicity to normal cells), and the property of not easy to produce bacteria resistance.All of these advantages will make the membrane-active peptides promising prospects in practices.α-helical cationic amphipathic peptides are a large class of membrane-active peptides with a typicalα-helical structure, which have a good amphipathicity with a perfect hydrophobic face and a complete hydrophilic face. Reasearches have been carried on theα-helical cationic amphipathic peptides, from the initial amino acid compositions to the structural parameters, until now the mechanism of the biological activity. Now, various strategies and multifarious methods are used to do a comprehensive and in-depth interpretation of membrane-active peptides in many ways and angles by researchers. By this mean, researchers expect to find more and better clinical applications of membrane-active peptides which are very important for human health.Factors affect activities of the membrane-active peptides hve been identified, including helicity, amphipathicity, hydrophobicity, charge, and self-association ability. In this thesis, we chose to alter the peptie ohelicity to study the relationship between the structure and function, which may play a guiding role ofα-helical peptide molecular design and modification, and thus can be used to screen the peptide analogs with low toxicity and high activity of bioactive peptides.In the design of peptides, we changed the helicity of peptides through amino acid substitutions. The degrees of helicity of peptide analogs were mearused under two diff ierent solutions by circular dichroism spectroscopy. Hydrophobicity of peptide molecules has been determined by use of RP-HPLC. Determination of the self-association of peptides was carried out by RP-HPLC temperature profiling technology. HCV production and infection assay and Pseudotyped HIV antiviral assay were utilized to study the antiviral ability of antivirus peptides, MTT assay was used for Hela cell line to determine the activity of killing tumor cells of anticancer peptides, The antibacterial activity of antibacterial peptides was also determined. The toxicity of the peptides against normal cells was mearsured by the ability of peptides lysing human red blood cells; the selectivity of biological activity of peptides was determined by the calculation of therapeutic index.In these thesis, we have shown that increaseing the helicity of antiviral peptide can improve the selectivity of peptides against viruses compared with the eukaryotic cells. The toxicity ofα-helical anticancer peptides against human red blood cells decreased with the reduction of peptide helicity. In addition, there is an optimal value between the helicity and biological activity of anticancer peptides, the helicity lower or higher than the optimum value will cause the decrease of its ability to kill cancer cells. Anti-bacterial growth assay showed that weaker helicity of antibacterial peptides can increase its antibacterial activty, however there is also an optimal range of the reduction of helicity, antimicrobial activity of the peptides was lost when decreaseing the helicity too much.