Extension of cell membrane boosting squalene production in the engineered Escherichia coli

Squalene is a lipophilic and non-volatile triterpene with many industrial applications for food, pharmaceuticals, and cosmetics. Metabolic engineering focused on optimization of the production pathway suffer from little success in improving titers because of a limited space of the cell membrane accommodating the lipophilic product. Extension of cell membrane would be a promising approach to overcome the storage limitation for successful production of squalene. In this study, Escherichia coli was engineered for squalene production by overexpression of some membrane proteins. The highest production of 612 mg/L was observed in the engineered E. coli with overexpression of Tsr, a serine chemoreceptor protein, which induced invagination of inner membrane to form multilayered structure. It was also observed an increase in unsaturated fatty acid in membrane lipids composition, suggesting cellular response to maintain membrane fluidity against squalene accumulation in the engineered strain. This study potentiates the capability of E. coli for squalene production and provides an effective strategy for the enhanced production of such compounds.     

The Effect of TCM-Induced HAMP on Key Enzymes in the Hydrolysis of AD Model Cells

Neurochemical Research - Alzheimer’s disease (AD) process is characterized classically by two hallmark pathologies: β-amyloid (Aβ) plaque deposition and neurofibrillary tangles of...     

Developing a Novel Gene-Delivery Vector System Using the Recombinant Fusion Protein of Pseudomonas Exotoxin A and Hyperthermophilic Archaeal Histone HPhA

Non-viral gene delivery system with many advantages has a great potential for the future of gene therapy. One inherent obstacle of such approach is the uptake by endocytosis into vesicular compartments. Receptor-mediated gene delivery method holds promise to overcome this obstacle. In this study, we developed a receptor-mediated gene delivery system based on a combination of the Pseudomonas exotoxin A (PE), which has a receptor binding and membrane translocation domain, and the hyperthermophilic archaeal histone (HPhA), which has the DNA binding ability. First, we constructed and expressed the rPE-HPhA fusion protein. We then examined the cytotoxicity and the DNA binding ability of rPE-HPhA. We further assessed the efficiency of transfection of the pEGF-C1 plasmid DNA to CHO cells by the rPE-HPhA system, in comparison to the cationic liposome method. The results showed that the transfection efficiency of rPE-HPhA was higher than that of cationic liposomes. In addition, the rPE-HPhA gene delivery system is non-specific to DNA sequence, topology or targeted cell type. Thus, the rPE-HPhA system can be used for delivering genes of interest into mammalian cells and has great potential to be applied for gene therapy.     

Nitrosothiol Formation and Protection against Fenton Chemistry by Nitric Oxide-induced Dinitrosyliron Complex Formation from Anoxia-initiated Cellular Chelatable Iron Increase

Dinitrosyliron complexes (DNIC) have been found in a variety of pathological settings associated with ^•NO. However, the iron source of cellular DNIC is unknown. Previous studies on this question using prolonged ^•NO exposure could be misleading due to the movement of intracellular iron among different sources. We here report that brief ^•NO exposure results in only barely detectable DNIC, but levels increase dramatically after 1–2 h of anoxia. This increase is similar quantitatively and temporally with increases in the chelatable iron, and brief ^•NO treatment prevents detection of this anoxia-induced increased chelatable iron by deferoxamine. DNIC formation is so rapid that it is limited by the availability of ^•NO and chelatable iron. We utilize this ability to selectively manipulate cellular chelatable iron levels and provide evidence for two cellular functions of endogenous DNIC formation, protection against anoxia-induced reactive oxygen chemistry from the Fenton reaction and formation by transnitrosation of protein nitrosothiols (RSNO). The levels of RSNO under these high chelatable iron levels are comparable with DNIC levels and suggest that under these conditions, both DNIC and RSNO are the most abundant cellular adducts of ^•NO.