Difference between revisions of "Part:BBa K118023:Experience"

Revision as of 14:28, 19 October 2019

This experience page is provided so that any user may enter their experience using this part.
Please enter how you used this part and how it worked out. Cellulomonas fimi uses 3 endoglucanases (including CenA, accession M15823) and an exoglucanase in the degradation of cellulose into cellobiose, before using beta-glucosidase to catalyse the conversion of cellobiose to D-glucose. This part was codon optimized for the expression in Caulobacter crescentus and synthesized by IDT.

We improved the characterization of this part by optimizing the expression and attempted to express the enzyme on the surface layer of C.crescentus. We characterized the activity of the CenA insert in the C.crescentus s-layer. In initial activity analysis we saw no increased activity compared to wild type RsaA protein indicating that either the protein insert as we designed it does not fold correctly in the surface layer, further cloning attempts and design alterations must be made to try to improve the results.

It likely did not work as the folding of the protein may have been disrupted by the insertion into the surface layer; we would have to try different designs of the protein insertion by using different insertion sites or cloning in a altered, truncated, version of the protein.

Applications of BBa_K118023

Further Improvement

• Group: [http://2019.igem.org/Team:CAU-China iGEM Team CAU-China 2019]
• Author: Siwen Liang and Xueshan Yan

Overview

We improved this part by fusing with INP-N (see BBa_K3279008), the INP-N fused endoglucanase (INP-CenA) can anchor in the cell membrane and function for surface display. The fusion protein was expressed and confirmed by SDS-PAGE(Figure 3), and the anchoring effect is measured through immunofluorescence staining and enzyme activity assay. We fused the INP with both CenA and Cex and conducted similar procedures.

Fig. 3 SDS-PAGE assay for fusion protein

Microscopy Observation

6His tag was added to the original protein CenA sequence as well as the fusion protein INP-CenA as the antigen to be targeted by the primary antibody. Logically, since the CenA-6His is originally expressed in the interior of the cell, we would not detect the fluorescence in the sample of CenA and Cex, while the fluorescence is detectable for INP-CenA-6His due to the cell membrane anchoring effect. We observed the E.coli cells expressing the original proteins (CenA and Cex)and the fusion proteins (INP-CenA and INP-Cex)under the fluorescence microscopy`s 20X objective (Figure 4) and confocal fluorescence microscopy`s 100X objective (Figure 5).

Fig. 4 E.coli cell immunofluorescence staining observation via fluorescence_microscopy 20x objective

Fig. 5 E.coli cell immunofluorescence staining observation via confocal fluorescence microscopy, 100x objective (images are local zoomed)

Under the same condition of 20X magnification and 355ms for exposure, we noted that the fluorescent signals of the unfused protein field are dimmer than those of the fusion protein field on average. To examine it more clearly, we observed the slices with the confocal fluorescence microscopy. The field of fusion protein samples showed that some foci are located on the borders of the cells, while this phenomenon was not observed in the field of the unfused protein samples. But due to the minuscule size of E.coli cells, our equipment falls short when trying to determine whether the fluorescent dot on a single cell is located on the outer membrane surface or not.

Fusion enzyme activity assay

The effect of fusion on enzyme activity was detected by measuring the cellulose degradation ability using CMC-Na as the substrate. We employed the procedures used by UESTC-China yet under the condition of citric acid-sodium citrate buffer with pH 4.8 and 50 ℃ for reaction temperature. We measured the cellulose degradation abilities of the supernatant of disrupted cell contents as well as the undisrupted cell suspensions. According to the standard curve of glucose concentration, we determined the activities of unfused enzymes CenA and Cex, and fusion enzymes INP-CenA and INP-Cex.(Figure 6)

Fig. 6 Enzyme activities assay (pH4.8 50℃)

From the data, we summarized that the cellulases` activities were not affected remarkably with the presence of INP-N. Also, the difference of enzyme activities between the ultrasonic-disrupted samples and undisrupted samples provided another evidence of the anchoring effect of INP-N. Since the fusion protein is anchored in the outer membrane surface, which would appear in the sediments after centrifugation，the samples of suspension with fused cellulases showed the relatively low level of the activity, compared with samples of unfused ones.

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