Efficient production of soluble human beta-defensin-3–4 fusion proteins in Escherichia coli cell-free system

Human β-defensins: The multi-functional natural peptide

The increasing threat of antibiotic resistance among pathogenic microorganisms and the urgent demand for new antibiotics require immediate attention. Antimicrobial peptides exhibit effectiveness against microorganisms, fungi, viruses, and protozoa. The discovery of human β-defensins represents a major milestone in biomedical research, opening new avenues for scientific investigation into the innate immune system and its resistance mechanisms against pathogenic microorganisms. Multiple defensins present a promising alternative in the context of antibiotic abuse. However, obstacles to the practical application of defensins as anti-infective therapies persist due to the unique properties of human β-defensins themselves and serious pharmacological and technical challenges. To overcome these challenges, diverse delivery vehicles have been developed and progressively improved for the conjugation or encapsulation of human β-defensins. This review briefly introduces the biology of human β-defensins, focusing on their multistage structure and diverse functions. It also discusses several heterologous systems for producing human β-defensins, various delivery systems created for these peptides, and patent applications related to their utilization, concluding with a summary of current challenges and potential solutions.

Enhanced functional expression of aquaporin Z via fusion of in situ cleavable leader peptides in Escherichia coli cell-free system

Aquaporin Z (AqpZ) is a water channel protein from Escherichia coli and has attracted many attentions to develop the biomimetic water filtration technology. Cell-free protein synthesis (CFPS) system, one of the most complex multi-enzymatic systems, has the ability of producing the integral membrane protein in vitro. To enhance the synthesis of AqpZ in E. coli cell-free system, several natural leader peptides were respectively fused at the N-terminus and were verified to enhance the expression level significantly. Moreover, the supplementation of detergents or liposome could activate leader peptidase from the cell-free extract and provide hydrophobic environment for proper folding of AqpZ. Thus, the release of mature AqpZ via the in situ removal of leader peptide was achieved, with a specific water transport activity of (2.1 ± 0.1) × 10⁻¹⁴ cm³ s⁻¹ monomer⁻¹. Using this in situ removable leader peptide strategy, the transcription-translation, leader sequence cleavage and membrane protein folding were integrated into a simple process in the cell-free system, providing a convenient approach to enhance the expression of target proteins, especially those membrane proteins difficult to achieve.

[Biological characteristics of defensin and its disease-resistance genetic engineering]

Defensin is a kind of cysteine-rich small peptide, which has a broad spectrum of resistance to bacteria with a special resistance mechanism. So far, a large number of studies on defensins have been reported, and the different types of defensins have been isolated from various organisms. A broad prospect of application on defensins has been displayed both in genetic engineering and medicine field. This article reviewed the classification and the biological characteristics of defensins, including mammalian α-, β-, θ-defensins, insect defensins, and plant defensins. The molecular structures, antibacterial activities, and antibacterial mechanisms of these definsins were summarized. The two mechanisms of de-fensin, including independent membrane mechanism and targeting of intracellular compounds by defensins, are ex-pounded. This paper also summarized the researches on isolation and expression of defensin genes and disease resistance genetic engineering of mammal and plant defensins. A prospect of the future applications of defensin both in biophar-maceutical sciences and plant disease resistance genetic engineering was discussed.

High-level expression of soluble subunit b of F1F0 ATP synthase in Escherichia coli cell-free system

The overexpression of subunit b of F(1)F(0) adenosine triphosphate (ATP) synthase from Escherichia coli is so toxic that it even prevents the transformation of plasmids encoding this protein into E. coli BL21 (DE3). In the present work, E. coli cell-free system was chosen as an alternative to express this highly toxic membrane protein. This protein was either produced as precipitates followed by detergent resolubilization or expressed as a soluble form with detergent addition. Among several types of tested detergents, Brij 58 could effectively solubilize approximately 85% of the target membrane protein within a wide range of concentration (48 to 178 times critical micelle concentration [CMC]) with little effect on the expression level. With the presence of Brij 58 at the final concentration of 96 times CMC in the E. coli cell-free system, 789 microg/mL of soluble subunit b was achieved after 4 h biosynthesis, which is the highest level for the expression of membrane proteins in a batch-mode cell-free expression system. The present work provides a rapid and efficient procedure of expressing one membrane protein with high cytotoxicity in the cell-free system and will be helpful to further exploration of reconstituting F(1)F(0) ATP synthase into liposome or polymer vesicle to design a nanoelectromechanical system device.