| Summary: | 碩士 === 國立中央大學 === 化學工程與材料工程研究所 === 99 === Cationic antimicrobial peptide –Indolicidin (IL) has been considered to be a potential antibiotic drug by its broad-spectrum of antibiotic activity against bacteria, fungi and even viruses. However, the hemolytic activity limits its clinical applications. To reduce its hemolytic activity, we had designed several less hemolytic Indolicidin analogues, IL-K7, IL-F89, IL-K7F89, through MD simulations in our previous work. But the mechanisms of its antibiotic and hemolytic behaviors are stIndolicidinl not clear. We had found that these peptides might oligomerized in aqueous solution and the degree of peptide oligomerization was consisted with their hemolytic activity. Therefore, we try to first study the possible structure of peptide oligomerization. And then the interactions between peptide oligomers and bio-mimic membranes are under investigation.
We studied the size of oligomer by gel electrophoresis and molecular dynamic simulation. The results showed that Indolicidin and its analogues might form dimer or trimer. We then studied the interaction between peptides and bio-mimic membranes by calcium dye leakage experiment. Two types of bio-mimic liposomes were made. One was made of pure POPC lipid of which the surface was neutral, the other was made of the mixture of POPC and POPG of which the surface was negatively charged. We found that both types of liposomes were perturbed by the peptides and the degree of dye release was increased with the amount of peptide added. Surprisingly, no dye leakage was observed when we test the peptide SAP, a well-known antimicrobial peptide of low hemolytic activity. The result indicated that the antimicrobial activity of SAP was not caused by cell membrane perturbation.
We further investigate the interaction between Indolicidin trimmers and bio-mimic membranes by all-atom molecular dynamic simulation. It was found that the Indolicidin trimmer dissociated and then re-associated in the POPC/POPG membrane. Simultaneously, we found that water molecules entered the hydrophobic core of membrane. The result supported the possibility of transient pore formation.
All the results indicated that Indolicidin and its derivatives might form dimmers or trimmers in the aqueous solution. The oligomers adsorbed onto the membrane and perturb the membrane structure. We considered that the membrane perturbation by peptide oligomers was related to the hemolytic behavior of these peptides.
|
|---|
