Improvement of expression level of polysaccharide lyases with new tag GAPDH in E. coli

Efficient Expression and Characterization of an Endo-Type Lyase HCLase_M28 and Its Gradual Scale-Up Fermentation for the Preparation of Chondroitin Sulfate Oligosaccharides

Glycosaminoglycan (GAG) lyases have been critical in structural and functional studies of GAGs. HCLase_M28, a lyase identified from the genome of Microbacterium sp. M28 was heterologously expressed, enzymatically characterized, and prepared in large-scale fermentation for the production of chondroitin sulfate (CS) oligosaccharides. Results showed that the expression of HCLase_M28 in Escherichia coli BL21 (DE3)-pET24a-HCLase_M28opt1 and Bacillus subtilis W800-pSTOP1622-HCLase_M28opt2 were 108-fold and 25-fold that of wide strain. The optimal lytic reaction of HCLase_M28 happened in 20 mM Tris-HCl (pH 7.2) at 50 °C with a specific activity of 190.9 U/mg toward CS-A. The degrading activity was slightly simulated in presence of 1 mM Ca2+ and Mn2+ while severely inhibited by Hg+, Cu2+, Fe3+, and SDS. TLC and ESI-MS analysis proved HCLase_M28 was an endolytic lyase and degraded CS and hyaluronic acid into unsaturated disaccharides. Through a gradual scale-up of fermentation in 5 L, 100 L, and 1000 L, a highly efficient intracellular expression of HCLase_M28 with an activity of 3.88 × 105 U/L achieved within a 34 h of cultivation. Through ultrafiltration, CS oligosaccharides with DP of 2 to 8 as the main components could be controllably prepared. The successful large-scale fermentation made HCLase_M28 a promising enzyme for industrial production of CS oligosaccharides.

A useful epitope tag derived from maltose binding protein

Maltose binding protein (MBP) is used in recombinant protein expression as an affinity and solubility tag. The monoclonal antibody B48 binds MBP tightly and has no cross-reactivity to other proteins in an Escherichia coli lysate. This high level of specificity suggested that MBP contains an epitope that could prove useful as a purification and visualization tag for proteins expressed in E. coli. To discover the MBP epitope, a co-crystal structure was determined for MBP bound to its antibody and four amino acids of MBP were identified as critical for the binding interaction. Fusions of various fragments of MBP to the glutathione S-transferase protein were engineered in order to identify the smallest fragment still recognized by the α-MBP antibody. Stabilization of the epitope via mutational engineering resulted in a minimized 14 amino-acid tag.

Engineering a thermostable chondroitinase for production of specifically distributed low-molecular-weight chondroitin sulfate

Chondroitinase ABC I (csABC I) has attracted intensive attention because of its great potential in heparin refining and the enzymatic preparation of low-molecular-weight chondroitin sulfate (LMW-CS). However, low thermal resistance (<30℃) restricts its applications. Herein, structure-guided and sequence-assisted combinatorial engineering approaches were applied to improve the thermal resistance of Proteus vulgaris csABC I. By integrating the deletion of the flexible fragment R166-L170 at the N-terminal domain and the mutation of E694P at the C-terminal domain, variant NΔ5/E694P exhibited 247-fold improvement of its half-life at 37℃ and a 2.3-fold increase in the specific activity. Through batch fermentation in a 3-L fermenter, the expression of variant NΔ5/E694P in an Escherichia coli host reached 1.7 g L^-1 with the activity of 1.0 × 10⁵ U L^-1 . Finally, the enzymatic approach for the preparation of LMW-CS was established. By modulating enzyme concentration and controlling depolymerization time, specifically distributed LMW-CS (7000, 3400, and 1900 Da) with low polydispersity was produced, demonstrating the applicability of these processes for the industrial production of LMW-CS in a more environmentally friendly way.

A novel protein purification strategy mediated by the combination of CipA and Ssp DnaB intein

Protein purification is an indispensable step in diverse fields of biological research or production process. Conventional purification methods including the affinity purification or the usage of self-aggregating tags suffered from many drawbacks such as the complicated steps, high cost and low efficiency. Moreover, the fusion tag usually had negative effects on the activity of the target protein. To address the above issues, here we propose a novel protein purification method which needs simple operation steps, and this method is mediated by the combination of CipA protein and a mini-intein (Synechocystis sp. PCC6803 DnaB, Ssp DnaB), depending on the assembly function of CipA and the self-cleavage function of Ssp DnaB. To realize the purification, CipA-DnaB-eGFP protein was expressed and assembled into protein crystalline inclusions (PCIs) in E. coli. Then, only cell lysis, cleavage and centrifugation steps were required to purify eGFP. Purified eGFP was in the supernatant with a purity of over 90%. The cleavage efficiency and the yield of eGFP reached 51.96% and 13.99 ± 0.88 mg/L fermentation broth, respectively. Furthermore, to broaden the application of this approach, three other proteins which were maltose binding protein (MBP), ketoisovalerate decarboxylase (Kivd) and alcohol dehydrogenase (AdhP) were purified with high cleavage efficiency. The purified Kivd and AdhP remained high specific activities. This work demonstrated an effective and convenient protein purification method.