Metal-Chelate Affinity Precipitation with Thermo-Responsive Polymer for Purification of ε-Poly-l-Lysine

Cell-penetrating activity of a short-chain ε-poly-l-α-lysine

Bacteria produce polycationic homopoly(amino acid)s, which are characterized by isopeptide backbones. We previously demonstrated that two representative bacterial polycationic isopeptides, ε-poly-l-α-lysine consisting of 25-35 l-α-lysine residues (ε-PαL25-35) and ε-poly-l-β-lysine consisting of l-β-lysine residues (ε-PβL4-13), were internalized into mammalian cells by both energy-independent direct penetration and energy-dependent endocytosis/macropinocytosis, and then diffused throughout the cytosol. In this study, we investigated the cell-penetrating activity of an ε-PαL short-chain derivative consisting of 5-14 l-α-lysine residues (ε-PαL5-14) to gain insight into the relationship between the isopeptide-chain length and the manner of cellular internalization. We prepared a conjugate of ε-PαL5-14 and a fluorescent dye (FAM) by click chemistry, and incubated the resulting polymer, ε-PαL5-14-FAM, with HeLa cells. Unlike ε-PαL25-35-FAM, ε-PαL5-14-FAM was internalized into cells only by energy-dependent endocytosis/macropinocytosis. Furthermore, a high concentration (>50 μM) was required for the internalization events. ε-PαL5-14 has a chain length almost equal to that of the membrane permeable ε-PβL4-13, which can enter cells at low concentrations. Considering that the basicity of the β-amino group is higher than that of α-amino acid at physiological pH, ε-PβL is expected to have a greater cell-penetrating capacity than ε-PαL, provided their isopeptide-chain lengths are similar, suggesting that a more extended chain derivative of ε-PβL would be more advantageous for cellular internalization of cargo proteins than ε-PαL25-35.

Biotechnological production and application of epsilon-poly-L-lysine (ε-PL): biosynthesis and its metabolic regulation

Epsilon-poly-L-lysine (ε-PL) is an unusual biopolymer composed of L-lysine produced by several microorganisms, especially by the genus Streptomyces. Due to its excellent antimicrobial activity, good water solubility, high safety, and biodegradable nature, ε-PL with a GRAS status has been widely used in food and pharmaceutical industries. In the past years, studies have focused on the biotechnological production of ɛ-PL, the biosynthetic mechanism of microbial ɛ-PL, and its application. To provide new perspectives from recent advances, the review introduced the methods for the isolation of ɛ-PL producing strains and the biosynthetic mechanism of microbial ɛ-PL. We summarized the strategies for the improvement of ɛ-PL producing strains, including physical and chemical mutagenesis, ribosome engineering and gene engineering, and compared the different metabolic regulation strategies for improving ɛ-PL production, including medium optimization, nutrient supply, pH control, and dissolved oxygen control. Then, the downstream purification methods of ɛ-PL and its recent applications in food and medicine industries were introduced. Finally, we also proposed the potential challenges and the perspectives for the production of ε-PL.

Epsilon-poly-L-lysine: Recent Advances in Biomanufacturing and Applications

ε-poly-L-lysine (ε-PL) is a naturally occurring poly(amino acid) of varying polymerization degree, which possesses excellent antimicrobial activity and has been widely used in food and pharmaceutical industries. To provide new perspectives from recent advances, this review compares several conventional and advanced strategies for the discovery of wild strains and development of high-producing strains, including isolation and culture-based traditional methods as well as genome mining and directed evolution. We also summarize process engineering approaches for improving production, including optimization of environmental conditions and utilization of industrial waste. Then, efficient downstream purification methods are described, including their drawbacks, followed by the brief introductions of proposed antimicrobial mechanisms of ε-PL and its recent applications. Finally, we discuss persistent challenges and future perspectives for the commercialization of ε-PL.

Extraction and purification of ε-poly-l-lysine from fermentation broth using an ethanol/ammonium sulfate aqueous two-phase system combined with ultrafiltration

ε-Poly-l-lysine (ε-PL) serves as a natural food preservative and is manufactured mainly by extraction from microbial fermentation broth using ion-exchange chromatography. In order to develop an alternative purification strategy, an environmentally friendly alcohol/salt aqueous two-phase system (ATPS) was explored in this study for ε-PL extraction. A study of the separation of ε-PL in different alcohol/salt systems showed that ethanol/ammonium sulfate ATPS exhibited the highest ε-PL partition coefficient and recovery ratio. Based on the phase diagram, the effect of phase composition on partition, and the removal of pigment and protein, an ATPS that was composed of 20% (w/w) ethanol and 20% (w/w) ammonium sulfate, with a feedstock at pH 9.5, was developed to extract ε-PL from the fermentation broth. This achieved an ε-PL recovery ratio of 96.15% with an ε-PL purity of 40.23% after triplicate extractions. Subsequently, desalting by ultrafiltration led to a final ε-PL product of 92.39% purity and 87.72% recovery. The ethanol/ammonium sulfate ATPS provides a new possibility for ε-PL purification.

Effect of ion form of the ion-exchange resin on ε-poly-l-lysine purification from microbial fermentation broth

ε-Poly-l-lysine (ε-PL) is an added-value natural product with widespread application in the fields of food, pharmaceuticals and biopolymer materials. However, the high production cost reduces its application. To improve the efficiency of ε-PL purification for decreasing the cost of downstream processes, the ion form of the ion-exchange resin, which is widely used for ε-PL purification, was investigated systematically in this study. Among eleven cation-exchange resins tested, the Amberlite IRC-50 resin offered the best adsorption capability and the highest desorption ratio. The adsorption kinetics of IRC-50 resin with H⁺, Na⁺ and NH₄ ⁺ ion forms followed a pseudo-second-order model. The dynamic adsorption and desorption parameters of ε-PL were optimized with a column packed with IRC-50 resin with Na⁺ and NH₄ ⁺. It is suggested that NH₄ ⁺ is the optimal ion form of IRC-50 resin for ε-PL extraction. Under optimal conditions, the IRC-50 resin with NH₄ ⁺ achieved the highest ε-PL adsorption capability, purity and recovery ratio of 307.96 mg g^-1, 76.52% and 96.2%, respectively. After further purification, a final ε-PL purity of 97.10% was achieved with a total recovery ratio of 66.01%. This is the first report on improving the ε-PL purification efficiency through optimizing the ion form of the ion-exchange resin. Moreover, it would offer guidance for other natural product recovery processes by ion-exchange chromatography.