Part:BBa_K3771097

SoxR-PsoxS-CSAD-6xHis

Description

This composite part consists of the soxR gene (BBa_K3771100), promoter P_soxS (BBa_K3771048), and the csad gene (BBa_K3771041), which encodes L-Cysteine sulfinic acid decarboxylase (CSAD). It is used to express CSAD to produce taurine under oxidative stress.

The soxR and the soxS gene are components of the soxRS regulon, which is important for E. coli to sense and respond to the oxidants. When SoxR protein is fully oxidized, it becomes a powerful transcription activator of the soxS promoter (P_soxS) (up to 100-fold), leading to the expression of the downstream gene^[1].

The L-Cysteine sulfinic acid decarboxylase is an enzyme that catalyzes the decarboxylation of L-Cysteine sulfinic acid (cysteine sulfinate) into hypotaurine, which is spontaneously oxidized to taurine. In order to use anti-polyhistidine-tag antibodies to detect the production of CSAD by western blot, we add 6xHis-tag at the C-terminal of CSAD.

Usage and Biology

This composite part was ligated with the pSAA vector and transformed into E. coli. We conducted colony PCR to verify whether E. coli uptake the correct plasmid. The size of the PCR product was as expected.

Fig. 1. The electrophoresis result of colony PCR. M: Marker; Lane 1: pSAA-soxR-P_soxS-sfgfp (1050 bp); Lane 2, 3: pSAA-soxR-P_soxS-csad-6xHis (1829 bp).​

After the overnight incubation of E. coli with our plasmid, we diluted the bacteria culture and measured OD₆₀₀ once in a while. Until OD₆₀₀ reached 0.5, we added 0.5 mM paraquat, which served as an oxidative stress inducer, into the culture. We collected 1 ml culture each from the control group and the paraquat group at 2, 4, 6 hours after paraquat was added. Afterward, we conducted SDS-Page and western blot to confirm paraquat was added. Afterward, we conducted SDS-Page and western blot to confirm whether CSAD expressed successfully under oxidative stress with the regulation of SoxR and P_soxS. With the presence of SoxR, the expression level of CSAD in the paraquat group is high enough to be detected in western blot, but still insufficient to be seen on SDS-Page (Fig. 2 & 3).

Fig. 2. The SDS-Page result. CSAD (~55 kDa); –: control; PQ: 0.1 mM paraquat.

Fig. 3. The western blot result. CSAD (~55 kDa); –: control; PQ: 0.1 mM paraquat.

References

1. Pomposiello PJ, Demple B. Redox-operated genetic switches: the SoxR and OxyR transcription factors. Trends Biotechnol. 2001;19(3):109-114. doi:10.1016/s0167-7799(00)01542-0

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
  INCOMPATIBLE WITH RFC[25]

  Illegal AgeI site found at 834
  
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal BsaI.rc site found at 619