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traI (K34G, Q63G)

Sequence and Features

The gene traI(K34G, Q63G) is derived from Agrobacterium tumefaciens and encode a enzyme necessary for synthesizing Quorum Sensing signaling molecules ([N-]acyl-homoserine lactones, AHLs), 3OC8 HSL (hereafter C8), in E. coli.

The mutation was introduced wild type traI(BBa_K553001).

The DNA sequences of traI (K34G, Q63G) is optimized for expressing in E. coli considering the codon usage

Characterization and improvement

In our wiki page ([http://2017.igem.org/Team:TokyoTech/Experiment/TraI_ TraI Assay]), we describe that the productivity of 3OC8HSL in E. coli heavily depends on the culture temperatures. However, to complete our co-culture system, the current C8 productivity at 37℃ was not enough to transmit the AHL signal to mammalian cells; note that mammalian cells are usually grown at 37℃. Therefore, we tried to mutate the traI gene(BBa_K553001) and increase the productivity of 3OC8HSL at 37℃.

Figure 1:' Sequence of traI wild type gene and mutant.
The mutations were introduced to the pSB1C3-based traI plasmid using the inverse-PCR method, and successful introduction of the mutations were confirmed with Sanger sequencing.

TraI has not been characterized so extensively, and thus, it is unclear what kind of mutations is appropriate for the above purpose. A preceding study describes that, in the case of LuxI, the amino acid substitution at the 34th and 63rd positions (both are substitutions from glutamate to glycine; E34G and E63G) increase the productivity of C6 ^[1]. Since TraI has homology to LuxI over the entire amino acid sequences, we speculate that the same amino acid substitutions in TraI can increase the productivity of 3OC8HSL. The sequences of traI mutants and wild-type are shown in Figure 1.

In the experiments shown in this page, one additional modification was made in experimental conditions; 1 μM of SAM (S-adenosylmethionine; structure is shown in Figure 5) was added to the culture of the Sender. Since 3OC8HSL is synthesized from SAM and ACP (acyl carrier protein) through the action of TraI in bacterial cells ^[2], we expected that the addition of SAM may increase the productivity.

Result

Figure 1: 3OC8HSL production of TraI wild type and mutant
Sender E. coli(producing TraI) were grown at 37℃ in liquid LB medium with 1μM of SAM. E. coli introduced empty vector was used as Negative Control.

The result of C8 production using the wild type TraI and mutants is shown in Figure 6. The RFU value of the TraI (K34G,Q63G)-expressing cells was approximately 1.9-fold higher than that of the TraI-expressing cells.

For more information, visit our page: [http://2017.igem.org/Team:TokyoTech/Experiment/TraI_Improvement TraI_Improvement page].

Material and Method

Materials

Strains
Reporter
・DH5α
Sender E.coli
・DH5α
・MG1655hapB
Medium
・LB medium
containing 1μM of SAM
・LB medium containing antibiotics
Dissolve antibiotics in LB medium (Ampicillin 50μg/mL, Chloramphenicol 34μg/mL, Kanamycin 50μg/mL)

Method

Supernatant Assay
1. Grow the Sender in LB medium containing 1μM of SAM for about 15 hours at 37℃.
2. Harvest the cells by brief centrifugation
3. Perform the same procedure as the reagent assay process (1~4) to prepare Reporter culture.
4. Mix 250 μL of the supernatant of Sender culture with Reporter culture in a microtube.
5. Incubate the microtube for 5 hours with gentle shakingat 37℃.
6. Take 100 μL of the culture and measure fluorescence intensity (excitation and emission wave lengths are 495 and 520 nm, respectively) and turbidity (measurement wavelength is 600 nm).
7. Calculate RFU dividing fluorescence intensity by turbidity and minus control value.

Reference

[1] Pavan Kumar Reddy Kambam, Daniel J. Sayut, Yan Niu, Dawn T. Eriksen, Lianhong Sun (2008) Directed evolution of LuxI for enhanced OHHL production. Biotechnology and Bioengineering Volume 101, Issue 2 1 October 2008 Pages 263-272

[2] MATTHEW R. PARSEK, DALE L. VAL, BRIAN L. HANZELKA, JOHN E. CRONAN, E. P. GREENBERG (1999) Acyl homoserine-lactone quorum-sensing signal generation. Proc. Natl. Acad. Sci. USA Vol. 96, pp. 4360-4365, April 1999 Biochemistry