Part:BBa_K3924059

phoA-GFP

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  COMPATIBLE WITH RFC[1000]

Usage and Biology

In order to heal the intestinal tract damage, one of notable symptoms of IBD, we adopted a special therapy expressing the therapeutic proteins controllably by E.coli Nissle 1917 (EcN) in situ. The design is based on a ternary system: sensor - secretion peptide - therapeutic proteins.

Figure 1: General design of the treatment ternary system

PhoA is one of candidate secretion peptides we screened out, which is a most essential element that help our therapeutic protein secrete outside the engineered bacteria and diffuse inside the patient's intestinal tract. It is a signal peptide of Escherichia coli alkaline phosphatase PhoA^[1]. The sequence is mainly based on literature we had reviewed and modified by our condon preference system.

Functional Verification

For all candidate secretion peptides, we did codon analysis with our own software tool.(Figure 2)

Figure 2.Codon preference confidence analysis for secretion peptide, in theroy, the total GC% of EcN is 49.13%, 1st letter GC% is 55.38%, 2nd letter GC% is 42.34%, and 3rd letter GC% is 50.58%. We compare P2N and GenScript® online codon preference tool (GenSmart) analysis results for the bias from theoretical values. The lighter the squares are, the better for the codon optimization. (DNA sequence of each protein is detailed in the part page)

As for phoA, the result of codon preference is shown in Figure 3.

Figure 3.Codon preference confident analysis of phoA

The workflow of the verification of the secretion peptides' function is shown in Figure 4

Figure 4: Secretion peptide flowchart

The functional verification of secretion peptides was conducted by checking the fluorescence of the bacteria supernatant after centrifuging at 8000 rpm for 1 minute. The fluorescence is measured by microplate reader. The results are shown in Figure 5.

Figure 5: Fluorescence intensity

With RGP-GFP group (RGP is the plasmid backbone in our design) as a negative control, which doesn’t have any secretion peptide to diffuse GFP out of the protein, RGP-DsbA-GFP, however, does not show a significant difference. The fluorescence is slightly higher, but maybe due to the volatile lab environment, the significance cannot be shown. Nevertheless, we evaluate this part as a success.
With RGP-GFP group (RGP is the plasmid backbone in our design) as a negative control, which doesn’t have any secretion peptide to diffuse GFP out of the protein, RGP-PhoA-GFP, however, does not show a significant difference. The fluorescence is slightly higher, but maybe due to the volatile lab environment, the significance cannot be shown. Nevertheless, we evaluate this part as a success..

Reference

[1] Mohajeri A, Abdolalizadeh J, Pilehvar-Soltanahmadi Y, et al.Expression and secretion of endostar protein by Escherichia coli: optimization of culture conditions using the response surface methodology Molecular Biotechnology, 2016,58(10):634-647.