Engineering versatile protein expression systems mediated by inteins in Escherichia coli

Biomaterial-Based bFGF Delivery for Nerve Repair

Diseases in the nervous system are common in the human body. People have to suffer a great burden due to huge economic costs and poor prognosis of the diseases. Many treatment modalities are now available that can make recovery better. Managing nutritional factors is also helpful for such diseases. The basic fibroblast growth factor (bFGF) is one of the major nutritional factors, which plays a crucial role in organogenesis and tissue homeostasis. It plays a role in cell proliferation, migration, and differentiation, thereby regulating angiogenesis and wound healing and repair of the muscle, bone, and nerve. The study on how to improve the stability of bFGF to increase the treatment effect for different diseases has garnered tremendous attention. Biomaterials are the popular methods to improve the stability of bFGF because they are safe for the living body as they are biocompatible. Biomaterials can be loaded with bFGF and delivered locally to achieve the goal of sustained bFGF release. In the present review, we report different types of biomaterials that are used for bFGF delivery for nerve repair and briefly report how the introduced bFGF can function in the nervous system. We aim to provide summative guidance for future studies about nerve injury using bFGF.

Synergistic hydrolysis of filter paper by recombinant cellulase cocktails leveraging a key cellobiase, Cba2, of Cellulomonas biazotea

Cellulomonas biazotea, a Gram-positive cellulolytic bacterium isolated from soil, is capable of producing a complete cellulase complex exhibiting endoglucanase, exoglucanase, and cellobiase activities. Despite the presence of a full complement of all three types of cellulases, samples prepared from both cell lysates and culture media of C. biazotea showed only weak synergistic activities formed among the cellulase components, as reflected by their inefficient performance in filter paper hydrolysis. However, when the five previously characterized recombinant cellobiases of C. biazotea were mixed individually or in different combinations with recombinant enzyme preparations (CenA/Cex) containing an endoglucanase, CenA, and an exoglucanase, Cex, of another Cellulomonas species, C. fimi, the cellulase cocktails exhibited not only much higher but also synergistic activities in filter paper hydrolysis. Among the 5 C. biazotea cellobiases studied, Cba2 was shown to perform 2.8 to 3.8 times better than other homologous isozymes when acting individually with CenA/Cex. More noteworthy is that when Cba2 and Cba4 were added together to the reaction mixture, an even better synergistic effect was achieved. The filter paper activities resulting from Cba2 and Cba4 interacting with CenA/Cex are comparable to those obtained from some commercial fungal cellulase mixtures. To our knowledge, our results represent the first demonstration of synergistic effects on filter paper hydrolysis achieved using recombinant bacterial cellulases.

Protein Splicing of Inteins: A Powerful Tool in Synthetic Biology

Inteins are protein segments that are capable of enabling the ligation of flanking extein into a new protein, a process known as protein splicing. Since its discovery, inteins have become powerful biotechnological tools for applications such as protein engineering. In the last 10 years, the development in synthetic biology has further endowed inteins with enhanced functions and diverse utilizations. Here we review these efforts and discuss the future directions.

Recombinant expression of insoluble enzymes in Escherichia coli: a systematic review of experimental design and its manufacturing implications

Recombinant enzyme expression in Escherichia coli is one of the most popular methods to produce bulk concentrations of protein product. However, this method is often limited by the inadvertent formation of inclusion bodies. Our analysis systematically reviews literature from 2010 to 2021 and details the methods and strategies researchers have utilized for expression of difficult to express (DtE), industrially relevant recombinant enzymes in E. coli expression strains. Our review identifies an absence of a coherent strategy with disparate practices being used to promote solubility. We discuss the potential to approach recombinant expression systematically, with the aid of modern bioinformatics, modelling, and ‘omics’ based systems-level analysis techniques to provide a structured, holistic approach. Our analysis also identifies potential gaps in the methods used to report metadata in publications and the impact on the reproducibility and growth of the research in this field.

Spontaneous Cleavages of a Heterologous Protein, the CenA Endoglucanase of Cellulomonas fimi, in Escherichia coli

CenA is an endoglucanase secreted by the Gram-positive cellulolytic bacterium, Cellulomonas fimi, to the environment as a glycosylated protein. The role of glycosylation in CenA is unclear. However, it seems not crucial for functional activity and secretion since the unglycosylated counterpart, recombinant CenA (rCenA), is both bioactive and secretable in Escherichia coli. Using a systematic screening approach, we have demonstrated that rCenA is subjected to spontaneous cleavages (SC) in both the cytoplasm and culture medium of E. coli, under the influence of different environmental factors. The cleavages were found to occur in both the cellulose-binding (CellBD) and catalytic domains, with a notably higher occurring rate detected in the former than the latter. In CellBD, the cleavages were shown to occur close to potential N-linked glycosylation sites, suggesting that these sites might serve as ‘attributive tags’ for differentiating rCenA from endogenous proteins and the points of initiation of SC. It is hypothesized that glycosylation plays a crucial role in protecting CenA from SC when interacting with cellulose in the environment. Subsequent to hydrolysis, SC would ensure the dissociation of CenA from the enzyme-substrate complex. Thus, our findings may help elucidate the mechanisms of protein turnover and enzymatic cellulolysis.

Efficient Generation of Hydrazides in Proteins by RadA Split Intein

Protein C-terminal hydrazides are useful for bioconjugation and construction of proteins from multiple fragments through native chemical ligation. To generate C-terminal hydrazides in proteins, an efficient intein-based preparation method has been developed by using thiols and hydrazine to accelerate the formation of the transient thioester intermediate and subsequent hydrazinolysis. This approach not only increases the yield, but also improves biocompatibility. The scope of the method has been expanded by employing Pyrococcus horikoshii RadA split intein, which can accommodate a broad range of extein residues before the site of cleavage. The use of split RadA minimizes premature intein N cleavage in vivo and offers control over the initiation of the intein N cleavage reaction. It is expected that this versatile preparation method will expand the utilization of protein C-terminal hydrazides in protein preparation and modification.

Novel strategy for expression of authentic and bioactive human basic fibroblast growth factor in Bacillus subtilis

Inteins, also known as "protein introns," have been found to be present in many microbial species and widely employed for the expression and purification of recombinant proteins in Escherichia coli. However, interestingly, until now there has not been much information on the identification and application of inteins to protein expression in Bacillus subtilis. In this article, for the first time, despite the likelihood of absence of inteins in B. subtilis, this bacterium was shown to be able to facilitate auto-catalytic cleavages of fusions formed between inteins and recombinant proteins. Employing a construct expressing the intein, Ssp DnaB, (DnaB), which was fused at its N-terminus with the cellulose-binding domain (CellBD) of an endoglucanase encoded by the cenA gene of Cellulomonas fimi, the construct was demonstrated to be capable of mediating intracellular expression of basic fibroblast growth factor (bFGF), followed by auto-processing of the CellBD-DnaB-bFGF fusion to result in bFGF possessing the 146-residue authentic structure. The mentioned fusion was shown to result in a high yield of 84 mg l^-1 of biologically active bFGF. Future work in improving the growth of B. subtilis may enable the use of this bacterium, working in cooperation with inteins, to result in a new platform for efficient expression of valuable proteins.

Intein mediated hyper-production of authentic human basic fibroblast growth factor in Escherichia coli

Human basic fibroblast growth factor is a functionally versatile but very expensive polypeptide. In this communication, employing a novel amplification method for the target gene and genetic optimization of a previously engineered expression construct, pWK3R, together with a refined fed-batch fermentation protocol, we report an achievement of a phenomenal yield of 610 mg/L of the 146 aa authentic human basic fibroblast growth factor (bFGF) in Escherichia coli. Construct pWK3R was first modified to form plasmid pWK311ROmpAd, which was devoid of the ompA leader sequence and possessed two copies of a DNA segment encoding a fusion product comprising an intein, Saccharomyces cerevisiae vascular membrane ATPase (VMA), and bFGF. When E. coli transformant JM101 [pWK311ROmpAd] was cultivated using the refined fed-batch fermentation protocol, superb expression resulting in a total yield of 610 mg/L of bFGF was detected. Despite existing in high levels, the bFGF remained to be soluble and highly bioactive.