Part:BBa_K4361103

BlcR with 6xHis-tag and TEV protease cleavage site

BlcR is a transcription factor originating from the bacterium Agrobacterium tumefaciens. A single BlcR monomer contains an effector binding domain near the C-terminus which recognizes the effectors, succinic semialdehyde (SSA) and gamma-Butyrolactone GBL, but also the rape drug gamma-hydroxybutyric acid (GHB). The N-terminal region allows for the dimerization of two BlcR monomers. Dimeric BlcR can bind to the blc <i/> operator sequence.
BlcR was originally added to the Parts Registry as Part:BBa_K1758370 by the Bielefeld-CeBiTec iGEM 2015 team. Their sequence for BlcR has been codon optimized for expression in <i>E.coli by us to improve expression of the protein (Part:BBa_K4361100). This composite part consists of codon-optimized BlcR, a 6xHis-tag for purification Part:BBa_K4361102, and a TEV cleavage site for removal of the tag from the protein (Part:BBa_K4361102). With this composite part, we were able to effectively produce and purify BlcR in E. coli .

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  INCOMPATIBLE WITH RFC[12]

  Illegal NheI site found at 766
  
• 21
  INCOMPATIBLE WITH RFC[21]

  Illegal BamHI site found at 901
  
• 23
  COMPATIBLE WITH RFC[23]
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal NgoMIV site found at 150
  
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal SapI.rc site found at 661
  

Usage and biology

BlcR is an allosteric transcription factor BlcR from the bacterium Agrobacterium tumefaciens. This plant bacterium is able to use GBL, a precursor of GHB, as an energy source. In the absence of GBL, GHB or SSA, BlcR will bind to the blc operator sequence Part:BBa_K4361000 and acts as a repressor for the transcription of the blc proteins. When GBL, GHB or SSA binds to BlcR, it is released from the DNA and the blcA, blcB and blcC proteins are transcribed and digest GBL to succinate ( Figure 1 ).

Figure 1. The regulatory mechanism of BlcR on the blc operon and the pathway from gamma-butyrolactone to succinic acid of Agrobacterium tumefaciens.

In our project we have designed a novel bioelectronic sensor for the detection of GHB in drinks by combining the specificity of the BlcR regulatory mechanism with the reliability of electronics. BlcR is tethered by dsDNA oligonucleotides carrying the blc operator sequence Part:BBa_K4361000 to the surface of a gold interdigitated electrode (IDE). We can measure the capacitance of the IDE, which is influenced by the protein molecules around the fingers of the electrode. If GHB enters the system, it will bind to BlcR, which will then release from the electrode causing the capacitance to increase. Electronic hardware will interpret the change in capacitance and produce an output signal to warn the user that their drink has been spiked.

Experimental results

Wet Lab module 1 focused on optimizing the expression and purification of BlcR. After applying the engineering cycle multiple times, a protocol was developed which allowed for the expression and relatively high yield of the protein. After expression in E. coli BL21(DE3) cells, the protein was captured on a His column with Ni-NTA beads and subsequently washed off through TEV digestion. The washed off solution was then further purified with size exclusion.

The functionality of this part was later proven in experiments with the BlcR-binding DNA oligos, see Part:BBa_K4361000 through Part:BBa_K4361022 and our results for module 3.