Understanding How the Antimicrobial Peptide Thanatin Interacts with the Lipid Bilayer of Cell Walls Using Model Membranes

Isolation and purification of a novel antimicrobial peptide from Porphyra yezoensis

We aimed to isolate antimicrobial peptides from Porphyra yezoensis. Enzymatic hydrolysate of P. yezoensis was purified by ultrafiltration, molecular sieve chromatography, and ion exchange chromatography sequentially. A novel peptide with strong antimicrobial activity against Staphylococcus aureus was isolated and the amino acid sequence was identified to be Thr-Pro-Asp-Ser-Glu-Ala-Leu (TPDSEAL). Physical and chemical properties and antimicrobial activity of the peptide were determined. The antimicrobial mechanism was studied. The antimicrobial activity of TPDSEAL kept stable under acidic or basic conditions, high temperature, and ultraviolet radiation. The antimicrobial mechanism of antimicrobial peptides may damage the cell wall and membrane, and enhance the permeability of cells, which leads to the outflow of intracellular substances and death of bacteria. This study provides novel insight into the preparation of marine-derived antimicrobial peptides. PRACTICAL APPLICATIONS: Antimicrobial peptides, which act as defensive weapons against microbes, have been broadly used as food additives in food industry. Due to the limited amount of natural antimicrobial peptides in organisms and the high cost of chemical synthesis, producing novel natural antimicrobial peptides with bioengineering methods has become an urgent task. In the present study, we prepared a novel antimicrobial peptide from pepsin-digested hydrolysate of Porphyra yezoensis using ultrafiltration, molecular sieve chromatography, ion exchange chromatography, and mass spectrometry analysis. A novel peptide with strong antimicrobial activity against Staphylococcus aureus was isolated and the amino acid sequence was identified to be Thr-Pro-Asp-Ser-Glu-Ala-Leu (TPDSEAL). The identified peptide exhibits great stability under acidic or basic conditions, high temperature, and ultraviolet radiation. Mechanism revealed that TPDSEAL treatment may damage the cell wall and membrane, enhance the permeability of cells, and lead to the death of bacteria. Our study provides the novel insight into the preparation of marine-derived antimicrobial peptides.

Thanatin confers partial resistance against aflatoxigenic fungi in maize (Zea mays)

Aflatoxin-producing fungi can contaminate plants and plant-derived products with carcinogenic secondary metabolites that present a risk to human and animal health. In this study, we investigated the effect of antimicrobial peptides on the major aflatoxigenic fungi Aspergillus flavus and A. parasiticus. In vitro assays with different chemically-synthesized peptides demonstrated that the broad-spectrum peptide thanatin from the spined soldier bug (Podisus maculiventris) had the greatest potential to eliminate aflatoxigenic fungi. The minimal inhibitory concentrations of thanatin against A. flavus and A. parasiticus were 3.13 and 12.5 µM, respectively. A thanatin cDNA was subsequently cloned in a plant expression vector under the control of the ubiquitin-1 promoter allowing the recombinant peptide to be directed to the apoplast in transgenic maize plants. Successful integration of the thanatin expression cassette was confirmed by PCR and expression was demonstrated by semi-quantitative RT-PCR in transgenic maize kernels. Infection assays with maize kernels from T1 transgenic plants showed up to three-fold greater resistance against Aspergillus spp. infections compared to non-transgenic kernels. We demonstrated for the first time that heterologous expression of the antimicrobial peptide thanatin inhibits the growth of Aspergillus spp. in transgenic maize plants offering a solution to protect crops from aflatoxin-producing fungi and the resulting aflatoxin contamination in the field and under storage conditions.