[Study on the interaction mechanism of antimicrobial peptide Cecropin-XJ in Xinjiang silkworm and Staphylococcus aureus DNA by spectra].

Nowadays many of antimicrobial peptides have been extensively studied in order to elucidate their antimicrobial mode of action. Much of the research focused on mechanisms of cytoplasmic membrane disruption has been proposed for antimicrobial peptides, but it is not known whether their antimicrobial mode of action is due to their effects on bacterial chromosome. To obtain more information about the possible mechanisms, Cecropin-XJ, a kind of antimicrobial peptide from Xinjiang silkworm, was used as subject and prepared by purification of Pichia yeast fermentation containing cecropin-XJ gene expression product. Subsequently, ultraviolet absorption spectra were employed to investigate whether this antibacterial function is due to Cecropin-XJ works on S. aureus DNA in vitro. The increase in absorbance of DNA samples at 260nm due to the addition of Cecropin-XJ was measured. It is called hyperchromicity of DNA, which can provide a direct measure of the degree of base-pair unstacking. The unstacking results in the loss of duplex helix, and then leads to the duplex helix becoming relaxing. At the same time, the interaction mode was studied by using ethidium bromide (EB) as an extrinsic fluorescence probe. With the addition of Cecropin-XJ, the intensity of intrinsic fluorescence absorbance of DNA at 307 nm increases greatly. It is suggested that the addition of Cecropin-XJ may unstack base-paire of DNA exposing the fluorescent amino acide, leading to the enhancing of DNA fluorescence intensity. Subsequently the competition between Cecropin-XJ and EB to combine with DNA was found. It is suggested that the style was groove binding and intercalation in the interaction of Cecropin-XJ and double helix DNA. Furthermore, in this study, the binding constant and binding number of Cecropin-XJ complex with DNA were determined. There were different binding constant and number of EB complex with DNA because of the the addition of Cecropin-XJ. It is showed that the interaction of Cecropin-XJ and DNA was based on intercalation or non-intercalation. Meanwhile, these results help explain the molecule mechanism of antimicrobial peptide from the interaction style and structure characteristic of Cecropin-XJ and S. aureus DNA. These findings could contribute to further investigation on the mechanism of action of Cecropin-XJ.