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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% α-helix, 21.6% β-sheet, 31.2% β-turns, and 47.2% random coils. Further, the study was focused on understanding the mode of action of caP4 against E. coli. At 8 µg/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 µg/ml showed disorientation of the membrane surface. Cetyl pyridinium chloride (CPC, 10 µg/ml-IC50), Mitomycin C (10 µg/ml-IC50), Colchicine (25 µg/ml-IC50), Cytochalasin B (30 µg/ml-IC50) and Cibacron blue (25 µg/ml-IC50) were used as cell growth inhibitors with or without caP4 (8 µg/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.

The present investigation reports the sequence of a 2.97KDa low molecular weight, cationic antibacterial peptide, caP4 isolated from wild variety of turmeric, Curcuma pseudomontana L. (Zingiberaceae). The rp-HPLC of 80% saturated ammonium sulphate protein precipitate showed four peaks labelled P1, P2, P3 and P4. The peak fraction, P4 eluted at 39.73 min showed 63.47% and 43.27% inhibition against E. coli and S. aureus respectively. The P4 was found to be stable at − 20 °C to 65 °C, in pH from 7.0 to 10.0 and retained antibacterial activity when treated with proteases. The MIC of P4 varied for different bacterial strains between 10 and 30 mg/L. Biofilm formation of P. aerugenosa and S. aureus was declined to 90% and 50% respectively at 20 µg of P4. The P4 on UPLC-MS yielded single major peak (with retention time of 1.98 min). The peak fraction was pooled and analysed using ESI-MS/MS, showing peptide masses ranging from 400 to 1800 Da. Further, Tof MS/MS-ESI of two intense peak yielded the sequences ASSCKPS (mass 1.16KDa) and ASSKWVAPSEW (mass 1.81 kDa) with a total mass of 2.97KDa, designated as caP4 (cationic peptide of Peak 4) having a net charge of +1 and hydrophobicity ranging from 18 to 22%. The above results show that caP4 could possibly be used as antibacterial peptide with significant therapeutic index.

Amino acids are known to possess variable efficacy against ulceration. Considering the good antiulcer activity of amino acids, a series of urea/thiourea derivatives of glutamic acid conjugated benzisothiazole analogue 3a–u with various substituents on aryl ring were synthesized, spectroscopically characterized and evaluated for in vitro H+/K+-ATPase inhibition. Majority of the compounds possessed potency compared to that of omeprazole, a reference drug. In particular, methoxy derivatives 3p–u were the most active compounds possessing a significant 15-fold increase for para substituent thus, contributing positively to gastric H+/K+-ATPase inhibition.