Green fluorescent protein and factorial approach: An effective partnership for screening the soluble expression of recombinant proteins in Escherichia coli

Improving the heterologous expression of human β-defensin 2 (HBD2) using an experimental design

At present, expressing antimicrobial peptides in bacterial models is considered a routine lab bench work. However, low expression yields of these types of proteins are usually obtained. In this work, the antimicrobial peptide human β-defensin 2 (HBD2) was obtained in low expression yields in Escherichia coli BL21(DE3). To improve the expression yields of HBD2, some variables such as cell density, temperature, and length of induction, as well as the inducer concentration, were investigated using a 2⁴-factorial design of experiments (DoE). This approach allowed us to identify the identification of critical variables (main effects and interactions among factors) affecting bacterial HBD2 expression. After the evaluation of 19 different combination, the best condition to express HBD2 had a pre-induction temperature of 37 °C, a cell density of 1.0 U (600 nm), an induction temperature of 20 °C and a 0.1 mM of gene expression inducer (IPTG) over four hours. Under such conditions, the expression yield of the HBD2 peptide was one order of magnitude higher than the peptide expression performed initially.

Induction of T7 Promoter at Higher Temperatures May Be Counterproductive

Bacterial expression of recombinant proteins is the most popular and convenient method for obtaining large quantities of pure protein. The induction of T7 promoter with isopropyl-β-d-thiogalactopyranoside (IPTG) is widely used for expression of large quantities of proteins in Escherichia coli. It has been reported that basic T7 promoter is leaky and expresses cloned genes without induction. The effect of T7 promoter induction on expression of proteins at different temperature using flow cytometry has not yet been investigated. Green fluorescent protein (GFP) as a non-peptide tag can be used for protein solubility screening and for high-throughput optimization of expression conditions using flow cytometry. Therefore, flow cytometry was used to study the effect of induction on the expression of T7 promoter driven emerald GFP (emGFP) at various temperatures. We noticed that percentage of emGFP positive cells decreased instead of increasing upon induction at higher temperatures. Western blot analysis confirmed that the amount of total and soluble emGFP decreased in induced cells compared uninduced cells at higher temperatures. Our results indicate that induction of basic T7 promoter at higher temperature may not necessarily increase protein expression. While using a basic T7 promoter it is highly recommended to analyze the effect of induction on protein expression at various temperatures.

Cloning, expression, crystallization and preliminary X-ray studies of a superfolder GFP fusion of cyanobacterial Psb32

A fusion of Psb32 from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 (TePsb32) with superfolder GFP was created for enhanced solubility and improved detection and purification. The fusion protein readily formed large hexagonal crystals belonging to space group P6₁22. A full data set extending to 2.3 Å resolution was collected at the Swiss Light Source. The phase problem could be solved by using only the sfGFP fusion partner or by using GFP and AtTLP18.3 from Arabidopsis thaliana as search models. Based on this expression construct, a versatile library of 24 vectors combining four different superfolder GFP variants and three affinity tags was generated to facilitate expression and screening of fluorescent fusion proteins.

Explanatory chapter: troubleshooting recombinant protein expression: general

One of the most daunting problems for biochemists is the expression of recombinant proteins. Often, the host organism differs from the organism from which the gene coding for the protein of interest was derived. This article provides guidelines to determine whether or not protein expression is a problem, describes possible reasons for low protein expression, and covers several possible solutions. A protocol for measuring protein expression during E. coli cell growth and after induction is given. The reader should note that low protein expression is a complex problem that often stems from a variety of factors. Combinations of the solutions presented in this article may be required to solve a problem of protein expression. A brief overview of host cell expression systems is given, but the article primarily focuses on expression in E. coli as this is the most commonly used host organism. Some of the methods discussed here, however, may be applied to other expression systems.

Statistical approaches to maximize recombinant protein expression in Escherichia coli: a general review

The supply of many valuable proteins that have potential clinical or industrial use is often limited by their low natural availability. With the modern advances in genomics, proteomics and bioinformatics, the number of proteins being produced using recombinant techniques is exponentially increasing and seems to guarantee an unlimited supply of recombinant proteins. The demand of recombinant proteins has increased as more applications in several fields become a commercial reality. Escherichia coli (E. coli) is the most widely used expression system for the production of recombinant proteins for structural and functional studies. However, producing soluble proteins in E. coli is still a major bottleneck for structural biology projects. One of the most challenging steps in any structural biology project is predicting which protein or protein fragment will express solubly and purify for crystallographic studies. The production of soluble and active proteins is influenced by several factors including expression host, fusion tag, induction temperature and time. Statistical designed experiments are gaining success in the production of recombinant protein because they provide information on variable interactions that escape the "one-factor-at-a-time" method. Here, we review the most important factors affecting the production of recombinant proteins in a soluble form. Moreover, we provide information about how the statistical design experiments can increase protein yield and purity as well as find conditions for crystal growth.