Bioinformatics Analysis And Preliminary Study Of The Action Mechanism Of Antimicrobial Peptide CGA-N46 And Its Derived Peptides

CGA-N46 is an N-terminal derived peptide of Chromogranin A(CGA), which can inhibit a variety of pathogenic Candida. The physical and chemical properties and antibacterial activity of two derived peptides of CGA-N46 that called CGA-N16 and CGA-N12 were studied. A peptide which has higher antibacterial activity was filtered and its mechanism of action has been studied preliminary.Different numbers of amino acid residue at both terminus of CGA-N46 were cut off, and two derived peptides CGA-N16 and CGA-N12 were obtained. The results of bioinformatics analysis showed that CGA-N46 and its derived peptides were all hydrophilic proteins with α- helical structure, the isoelectric pointswere neutral or weak alkline. CGA-N12 had the highest thermal stability and the longest half-life time in mammalian and yeast.Circular dichroism(CD) was used to study the secondary structures of CGA-N46 and its derivatives in PBS,30 mM SDS solution and small unilamellar liposome solution.The bioinformatics software was used to make a fitting operation of the secondary structures of the peptides in different environmental conditions. The results showed thatα- helical structure were mainlythe secondary structure of CGA-N46 and its derived fragmentsin PBS and 30 mM SDS solution, while the the proportion of α-helix structure reduced and the proportion of other structures increased in small unilamellar liposome solution.The results of MTT assay showed that the antifungal activities of CGA-N16 and CGA-N12 were all higher than CGA-N46, CGA-N12 had the highest inhibitory activity and its most sensitive strain was Candida.tropical, with the MIC100 was 0.075mmol·L-1. But they all had no effects on bacteria.The results of scanning electron microscope showed that the surface of Candida tropicalis cells appear shrinked after the treatment of CGA-N12. The results of transmission electron microscope showed that the lacuna cavity between cell wall and cell membranenarrowed and darkened, the structures of organelles were broken. It was speculated tha the cell wall of Candida.tropicalwere broken after the trentment of CGA-N12, andthe soluble substances between cell wall and cell membrane lacuna leak out. CGA-N12 went into the lacuna through the cell wall cracks, and then passed through cellmembrane byconfiguration changes, anddestroyed the structures oforganelles, resulted in the cell death.In conclusion, CGA-N12 is a new antimicrobial peptide which has high antibacterial activity and high research value.