Antimicrobial peptides , as an integral part of the innate immune system, kill bacteria through a special mechanism of action, making them less susceptible to drug resistance. However, Lipopolysaccharide (LPS) as the permeation barrier on the bacterial membrane, inhibits the antibacterial activity of antimicrobial peptides and triggers the inflammatory response. GWKRKRFG is an LPS binding sequence with a β-boomerang motif that can be linked to antimicrobial peptides to enhance their LPS affinity and reduce the possibility of LPS-induced inflammatory responses. In this study, a series of hybrid peptides were designed by conjugating the reported LPS binding sequence to the C-/N-terminal sequences of the natural porcine antimicrobial peptide PMAP-23 to increase the LPS affinity of peptides. Among all the designed hybrid peptides, 4R-PP-G8 showed the best antibacterial activity, nonhemolytic activity, and excellent cell selectivity. The presence of LPS not only induced the secondary structure transformation of 4R-PP-G8 from a random structure to an α-helical structure but also reduced the antibacterial activity of 4R-PP-G8 in a dose-dependent manner, indicating the excellent binding ability of 4R-PP-G8 to LPS. The LPS/LTA binding assay further verified the interaction between the peptide and LPS. The membrane permeability test verified that 4R-PP-G8 possessed a strong capability to penetrate the bacterial membrane after interacting with LPS. More direct membrane disruption was observed under FE-SEM and TEM. In conclusion, we provided a simple and efficient method to improve the LPS binding ability of antimicrobial peptides and enhance their antimicrobial activity, resulting in the peptide 4R-PP-G8 with clinical application potential.
Jie He,Ming Duan,Shouwei Zhou,Liqiang Zhao,Zhifeng Luo,Shenwen Fang
The widespread use of polymer flooding has resulted in a large number of produced liquids consisting of crude oil emulsions and oily wastewater. Efficient flocculants are required to treat these produced liquids till the oily wastewater satisfies the requirements for reinjection formation in order to maintain the regular manufacturing process. In this work, an unsaturated polyether macromonomer (PEP-30) was prepared by ring-opening polymerization using isobutenol as a starting material. Subsequently, a novel flocculant (PMAP) was obtained by copolymerization of dimethylamino propylmethacrylamide (DMAPMA) and PEP-30. For the produced liquids with different crude oil emulsion content, the oil removal rate of PMAP at a dosage of 150 mg/L was more than 75%, and the oil removal rate and versatility were better than those of conventional cationic flocculants. Furthermore, the findings of the flocculation mechanism investigation demonstrated that PMAP had a low interfacial elastic modulus and a large interfacial adsorption mass. Specifically, the optical tweezers were used to detect the interaction force between oil droplets. PMAP effectively strengthened the attraction between oil droplets, extending their duration in contact during flocculation and promoting their coalescence.
Antimicrobial peptides are believed to be promising bio-preservatives to prevent microbial spoilage through food processing and preservation. With the aim of developing short peptides with broad-spectrum antimicrobial activity and revealing their potential antimicrobial mechanism, a novel class of dodecapeptides were designed by introducing Trp into the hydrophilic face of RI12, a truncated α-helical peptide of porcine myeloid antimicrobial peptide-36 (PMAP-36). The antimicrobial activity study indicated that Trp endowed the peptides with higher antimicrobial potency, and the net charge of +5 was sufficient for the dodecapeptides to exert antimicrobial action. Taking hemolytic activity into consideration, the most promising peptide RI12[K3W] (RLWKIGKVLKWI-NH2) was screened with high antimicrobial activity and non-toxicity. The antimicrobial mechanism study revealed that RI12[K3W] possessed the ability to bind to LPS components and enhance membrane permeability, which was verified by membrane penetration assays. Flow cytometry and electron microscopy further confirmed that RI12[K3W] killed bacterial cells primarily by membrane damage. The results guide the potential application of antimicrobial peptides in the food industry as food preservatives to prevent bacterial contamination.
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