Gel Protein Extraction's Impact on Conformational Epitopes of Linear Non-Tagged MPT64 Protein

The production and purification of recombinant proteins are crucial to acquiring pure MPT64 protein. Due to the fact that protein epitopes may undergo conformational changes during purification, this study, therefore, investigated an effective rapid purification method to produce highly intracellular pure MPT64 protein without causing conformational changes in the epitope under denaturing conditions. MPT64 was isolated from E. coli and electrophoresed using gel SDS-PAGE. Then, the desired protein bands were excised and purified with two methods: electroelution and passive elution. The isolated protein was identified via peptide mass fingerprinting using MALDI-TOF MS and reacted with IgG anti-MPT64, and the cross-reactivity of the isolated protein with IgY anti-MPT64 was confirmed using Western blot. The results show that both of these methods produced pure MPT64 protein, and the MPT64 protein was confirmed based on the MALDI-TOF MS results. Neither of these two methods resulted in epitope changes in the MPT64 protein so it could react specifically with both antibodies. The yield of MPT64 protein was higher with electroelution (2030 ± 41 µg/mL) than with passive elution (179.5 ± 7.5 µg/mL). Thus, it can be inferred that the electroelution method is a more effective method of purifying MPT64 protein and maintaining its epitope than the passive elution method.

Improving of pelB-Secreted MPT64 protein released by Escherichia coli BL21 (DE3) using Triton X-100 and Tween-80

pelB has been known as a successful signal peptide to translocate the protein target extracellularly in the Escherichia coli system. However, in our previous study, the yield of MPT64 protein extracellular recovery was still low and plenty of this protein was remain trapped in cytoplasm and periplasm. Recently, nonionic surfactants were efficiently reported to secrete recombinant protein extracellularly. Nonetheless, it must be clarified whether the surfactant supplementation can improve the yield of MPT64 extracellular protein significantly without giving impact on the structure of isolated MPT64 protein and can minimized the cell lysis effect. MPT64 protein secretion was carried out by comparing the effects of surfactants Tween 80 and Triton × 100 at various concentrations. Triton × 100 was able to increase the extracellular MPT64 protein gain up to 3 times higher than Tween 80 and it was in line with the greater level ratio of cell leakage of Triton × 100 compared to that of Tween 80. Similarly, the viable cell of the cultures decreased dramatically. However, both surfactants did not interfere the structure of MPT64 protein. In conclusion, Triton × 100 can be chosen as the supporting surfactant to assist the act of peptide signal in improving the resulting of MPT64 extracellular protein.

Comparison of simple and rapid extracting methods of free-tags Mycobacterium tuberculosis protein 64 Recombinant Protein from polyacrylamide gel: Electroelution and the optimized passive elution

In this study, the Mycobacterium tuberculosis protein 64 (MPT64) protein was constructed without any tags to facilitate the purification using column affinity chromatography, but the MPT64 must be obtained as a pure protein. This study was purpose to ensure the efficient extracting method to purify protein MPT64 directly from the polyacrylamide gel. The crude extract of extracellular protein containing MPT64 protein was separated into single protein band and the targeted protein which is located in the size of 24 kDa was excised. Each of the six bands was collected in a sterile microtube to be eluted using electroelution and the optimized of the passive-elution method. Both the elution methods demonstrated the purity level of the MPT64 protein by detecting a solely band on the gel at the 24 kDa. Among the variety of passive-elution time, the highest MPT64 protein concentration was 0.549 mg/ml after elution for 72 h. However, the electroelution result provided higher MPT64 protein concentration, i.e., 0.683 mg/mL. However, based on the recognition of the purified MPT64 protein on commercial detection kit of MPT64 protein, it showed that the positive result was only showed by the passive-elution extracting protein. Therefore, for purifying the protein MPT64 from the sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels, the efficient method was passive elution.

Real-time monitoring of rhamnose induction effect on the expression of mpt64 gene fused with pelB signal peptide in Escherichia coli BL21 (DE3)

In this research, Escherichia coli BL21 (DE3) harboring an expression vector constructed with a rhamnose-inducible promoter and a pelB signal peptide was used as a host cell to produce MPT64 protein. The objective of this research was to figure out the optimum time of mpt64 gene expression through real-time monitoring of MPT64 protein production and distribution in host compartments. The mpt64 expression was regulated by the rhamnose presence at a concentration of 4 mM. The real-time isolated protein was monitored using polyacrylamide gel electrophoresis in denaturation condition. Based on real-time monitoring, the MPT64 protein (24 kDa) in the cytoplasm was optimum detected at 24 h after induction. For periplasmic fraction, the protein was detected at 4 h after induction but thinning at 15 h after induction. At 16 h after induction, the MPT64 protein band was found in the medium with increasing concentrations until 24 h. Thus, it can be concluded that the mpt64 gene expression was regulated in the presence of rhamnose as an inducer, and the proteins were shown to be translocated throughout the host cell compartment with different levels of protein accumulation at different times, according to the role of pelB as a signal peptide.

Optimization of culture conditions for Mpt64 synthetic gene expression in Escherichia coli BL21 (DE3) using surface response methodology

MPT64 is a specific protein that is secreted by Mycobacterium tuberculosis complex (MTBC). The objective of this study was to obtain optimum culture conditions for MPT64 synthetic gene expression in Escherichia coli BL21 (DE3) by response surface methodology (RSM). The RSM was undertaken to optimize the culture conditions under different cultivation conditions (medium concentration, induction time and inducer concentration), designed by the factorial Box-Bhenken using Minitab 17 statistical software. From the randomized combination, 15 treatments and three center point repetitions were obtained. Furthermore, expression methods were carried out in the flask scale fermentation in accordance with the predetermined design. Then, the MPT64 protein in the cytoplasm of E. coli cell was isolated and characterized using sodium dodecyl sulfate polyacrilamide electrophoresis (SDS-PAGE) then quantified using the ImageJ program. The optimum conditions were two-fold medium concentration (tryptone 20 mg/mL, yeast extract 10 mg/mL, and sodium chloride 20 mg/mL), 5 h of induction time and 4 mM rhamnose. The average concentration of recombinant MPT64 at optimum conditions was 0.0392 mg/mL, higher than the predicted concentration of 0.0311 mg/mL. In conclusion, the relationship between the selected optimization parameters strongly influenced the level of MPT64 gene expression in E. coli BL21 (DE3).