Expression of soluble native protein in Escherichia coli using a cold-shock SUMO tag-fused expression vector

Catalytic efficiency and thermal stability promotion of the cassava linamarase with multiple mutations for better cyanogenic glycoside degradation

In our previous study, we found that cassava cyanogenic glycosides had an acute health risk. Therefore, to solve this problem, the improvement of specific degradation of cyanogenic glycosides of cassava linamarase during processing is the key. In this study, the catalytic activity and thermal stability of enzymes were screened before investigating the degradation efficiency of cyanogenic glycosides with a cassava linamarase mutant K263P-T53F-S366R-V335C-F339C (CASmut) -controlled technique. The CASmut was obtained with the optimum temperature of 45 °C, which was improved by 10 °C. The specific activity of CASmut was 85.1 ± 4.6 U/mg, which was 2.02 times higher than that of the wild type. Molecular dynamics simulation analysis and flexible docking showed there were more hydrogen bonding interactions at the pocket, and the aliphatic glycoside of the linamarin was partially surrounded by hydrophobic residues. The optimum conditions of degradation reactions was screened with CASmut addition of 47 mg/L at 45 °C, pH 6.0. The CASmut combined with ultrasonication improved the degradation from 478.2 ± 10.4 mg/kg to 86.7 ± 7.4 mg/kg. Those results indicating the great potential of CASmut in applying in the cassava food or cyanogenic food. However, challenges in terms of the catalytic mechanism research is worthy of being noticed in further studies.

Roles of conserved active site residues in the IscS cysteine desulfurase reaction

Escherichia coli cysteine desulfurase (CD), IscS, modifies basal metabolism by transferring sulphur (S) from L-cysteine to numerous cellular pathways, whereas NFS1, a human CD, is active only in the formation of the [Acp]₂:[ISD11]₂:[NFS1]₂ complex. Despite the accumulation of red-coloured IscS in E. coli cells as a result of the deficiency of accessible iron, as revealed in our previous studies, the mechanism of the potential enzymatic reaction remains unclear. In this study, the N-terminus of IscS was fused with the C-terminus of NFS1, which was reported to be almost fully active as IscS and exhibits a pyridoxal 5'-phosphate (PLP) absorption peak at 395 nm. Moreover, SUMO-EH-IscS exhibited significant growth recovery and NADH-dehydrogenase I activity in the iscS mutant cells. Furthermore, through in vitro and in vivo experiments combined with high-performance liquid chromatography and ultra-performance liquid chromatography-tandem mass spectrometry, it was shown that the new absorption peaks of the IscS H104Q, IscS Q183E, IscS K206A, and IscS K206A&C328S variants at 340 and 350 nm may correspond to the enzyme reaction intermediates, Cys-ketimine and Cys-aldimine, respectively. However, after mutation of the conserved active-site residues, additional absorption peaks at 420 and 430 nm were associated with PLP migration in the active-site pocket. Additionally, the corresponding absorption peaks of Cys-quinonoid, Ala-ketimine, and Ala-aldimine intermediates in IscS were 510, 325, and 345 nm, respectively, as determined by site-directed mutagenesis and substrate/product-binding analyses during the CD reaction process. Notably, red IscS formed in vitro by incubating IscS variants (Q183E and K206A) with excess L-alanine and sulphide under aerobic conditions produced an absorption peak similar to the wild-type IscS, at 510 nm. Interestingly, site-directed mutation of IscS with hydrogen bonds to PLP at Asp180 and Gln183 resulted in a loss of enzymatic activity followed by an absorption peak consistent with NFS1 (420 nm). Furthermore, mutations at Asp180 or Lys206 inhibited the reaction of IscS in vitro with L-cysteine (substrate) and L-alanine (product). These results suggest that the conserved active site residues (His104, Asp180, and Gln183) and their hydrogen bond with PLP in the N-terminus of IscS play a key role in determining whether the L-cysteine substrate can enter the active-site pocket and regulate the enzymatic reaction process. Therefore, our findings provide a framework for evaluating the roles of conserved active-site residues, motifs, and domains in CDs.

Characterization of Sphingobacterium sp. Ab3 Lipase and Its Coexpression with LEA Peptides

Sphingobacterium sp. is a yellowish Gram-negative bacterium that is usually characterized by high concentrations of sphingophospholipids as lipid components. As microbial enzymes have been in high demand in industrial fields in the past few decades, this study hopes to provide significant information on lipase activities of Sphingobacterium sp., since limited studies have been conducted on the Sphingobacterium sp. lipase. A microbe from one collected Artic soil sample, ARC4, was identified as psychrotolerant Sphingobacterium sp., and it could grow in temperatures ranging from 0°C to 24°C. The expression of Sphingobacterium sp. lipase was successfully performed through an efficient approach of utilizing mutated group 3 late embryogenesis abundant (G3LEA) proteins developed from Polypedilum vanderplanki. Purified enzyme was characterized using a few parameters, such as temperature, pH, metal ion cofactors, organic solvents, and detergents. The expressed enzyme is reported to be cold adapted and has the capability to work efficiently under neutral pH (pH 5.0 to 7.0), cofactors like Na+ ion, and the water-like solvent methanol. Addition of nonionic detergents greatly enhanced the activity of purified enzyme. IMPORTANCE The mechanism of action of LEA proteins has remained unknown to many; in this study we reveal their presence and improved protein expression due to the molecular shielding effect reported by others. This paper should be regarded as a useful example of using such proteins to influence an existing expression system to produce difficult-to-express proteins.

A simple and rapid protein purification method based on cell-surface display of SUMO-fused recombinant protein and Ulp1 protease

The development of novel methods for highly efficient protein purification remains a research focus in the biotechnology field because conventional purification approaches, including affinity purification, gel filtration, and ion-exchange chromatography, require complex manipulation steps and are costly. Here, we describe a simple and rapid protein purification strategy in which the SUMO tag and Ulp1 protease are surface-displayed separately on Escherichia coli cells. After protein induction, the cells are harvested, resuspended in cleavage buffer, and incubated together for cleavage. In this approach, the surface-displayed Ulp1 cleaves the membrane-anchored SUMO fusion protein, resulting in the release of the target protein from the C-terminal of SUMO into the solution. The bacterial cells harboring SUMO and Ulp1 on their surfaces can be easily removed by centrifugation. To evaluate the purification method, we used red fluorescent protein (mCherry). Purified mCherry protein (7.72 ± 1.05 mg from 1 L of bacterial culture) was obtained after only 30 min of incubation. The protein purity was higher than 80%, and could be further improved (> 90%) by simple ultrafiltration. This study offers a promising and simple strategy for the purification of recombinant protein in its native form that requires only cleavage and centrifugation steps.

Soluble expression of IGF1 fused to DsbA in SHuffle™ T7 strain: optimization of expression and purification by Box-Behnken design

Production of insulin-like growth factor 1 (IGF1) in Escherichia coli mostly results in the formation of inclusion bodies. In the present study, IGF1 was fused to disulfide bond oxidoreductase A (DsbA) and expressed in SHuffle™ T7 strain, in order to obtain correctly folded protein. Soluble expression and IMAC purification of DsbA-IGF1 were optimized by applying the Box-Behnken design of response surface methodology. The optimization greatly increased concentration of soluble protein from 317 to 2600 mg/L, and IMAC yield from 400 to 1900 mg/L. Results of ANOVA showed induction OD600 and temperature had significant effects on the soluble protein expression while isopropyl-β-d thiogalactoside, in the concentrations tested, displayed no significant effect. Moreover, the three parameters of the binding buffer including, pH, concentration of NaCl, and imidazole displayed significant effects on the IMAC yield. Then, purified DsbA-IGF1 was cleaved by human rhinovirus 3C protease, and authentic IGF1 was obtained in flow through of a subtractive IMAC. Final polishing of the protein by reversed-phase HPLC yielded IGF1 with purity of 96%. The quality attributes of purified IGF1 such as purity, identity, molecular size, molecular weight, secondary structure, and biological activity were assessed and showed to be comparable to the standard IGF1. The final yield of purified IGF1 was estimated to be 120 ± 18 mg from 1 L of the culture. Our results demonstrated a simple and easily scalable strategy for production of large amounts of bioactive IGF1 by rational designing soluble protein expression, and further optimization of expression and purification methods.