Mechanism of Antibacterial Cationic Peptide caP4 from Curcuma pseudomontana L. (Zingiberaceae) Against E. coli

Abstract

In our previous published article ( https://doi.org/10.1007/s10989-019-09883-7 ), caP4???a cationic peptide of 2.97 kDa from Curcuma pseudomontana L. (Zingiberaceae) with sequences ASSCKPS and ASSKWVAPSEW showed significant antibacterial activity against Escherichia coli and Staphylococcus aureus. In the present study, circular dichroism (CD) data of caP4 showed 0% ??-helix, 21.6% ??-sheet, 31.2% ??-turns, and 47.2% random coils. Further, the study was focused on understanding the mode of action of caP4 against E. coli. At 8 ??g/ml (MIC), caP4 permeabilized the cell membrane with maximum recorded at 50 min. Scanning electron microscopy analysis of E. coli cells with caP4 at 16 ??g/ml showed disorientation of the membrane surface. Cetyl pyridinium chloride (CPC, 10 ??g/ml-IC50), Mitomycin C (10 ??g/ml-IC50), Colchicine (25 ??g/ml-IC50), Cytochalasin B (30 ??g/ml-IC50) and Cibacron blue (25 ??g/ml-IC50) were used as cell growth inhibitors with or without caP4 (8 ??g/ml) to check the action of peptide intracellularly. E. coli cells with caP4 showed 100% cell death at 100 min. E. coli cells pre-treated with caP4 for 30 min showed 100% and 96% cell death at 60 min and 56 min with CPC and Mitomycin C respectively, suggesting that caP4 is acting by entering into the cell membrane and thus inhibit protein synthesis similar to CPC and Mitomycin C, whereas Colchicine, Cytochalasin B, Cibacron blue did not show significant cell death with pre and post-treatment of caP4. Thus, the study showed the synergistic effect of caP4 with cell growth inhibitors CPC and Mitomycin C in enhancing the antibacterial activity. Thus the data provide a new insight to understand the mechanism of antibiotic activity of caP4 and could lay the foundation for developing plant based antibacterial drugs in future to combat drug resistant microbes.