Part:BBa_K2933234

RBS a+Linker g+GST+Linker e+SHD

This part consists of RBS a, protein coding sequence(GST+Linker e+SHD), the RBS and the protein coding sequence can be connected by linker g. The biological module can be build into E.coli for protein expression. This part can be prefaced with promoters of different strengths and types to regulate expression function.

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
  INCOMPATIBLE WITH RFC[1000]

  Illegal SapI.rc site found at 113
  

Usage and Biology

This composite part is made up with five basic parts, the RBSa, the linker g and the GST tag, the cutting site of Prescission Protease and our target protein SHD. It encodes a protein which is SHD fused with GST tag. The fusion protein is about 55 kD. In order to gain the highly purified target protein, we add GST tag in N-terminal of SHD and combine the two parts with the cutting site of Prescission Protease. The fusion protein can be cut off at the cutting site by Prescission Protease. It is convenient for us to purify our target protein.

Molecular cloning

First, we used the vector pGEX-6p-1 to construct our expression plasmid. And then we converted the plasmid constructed to E. coli DH5α to expand the plasmid largely.

Figure 1. Left: The PCR result of SHD. Right: The verification results by enzyme digestion.

After verification, it was determined that the construction is successful. We converted the plasmid to E. coli BL21(DE3) for expression and purification.

Expression and purification

Pre-expression:
The bacteria were cultured in 5mL LB liquid medium with ampicillin(100 μg/mL final concentration) in 37℃ overnight.
Massive expressing:
After taking samples, we transfered them into 1L LB medium and add antibiotic to 100 μg/mL final concentration. Grow them up in 37°C shaking incubator. Grow until an OD 600 nm of 0.8 to 1.2 (roughly 3-4 hours). Induce the culture to express protein by adding 1 mM IPTG (isopropylthiogalactoside, MW 238 g/mol). Put the liter flasks in 16°C shaking incubator for 16h.

Affinity Chromatography:
We used the GST Agarose to purify the target protein. The GST Agarose can combine specifically with the GST tag fused with target protein.

• First, wash the column with GST-binding buffer for 10 minutes to balance the GST column.
  
• Second, add the protein solution to the column, let it flow naturally and bind to the column.
  
• Third, add GST-Washing buffer several times and let it flow. Take 10μl of wash solution and test with Coomassie Brilliant Blue. Stop washing when it doesn’t turn blue.
  
• Forth, add 400μL Prescission Protease (1mg/mL) to the agarose. Digest for 16 hours in 4℃.
• Fifth, add GST-Elution buffer several times. Check as above. Collect the eluted proteins for further operation.
  

Figure 2. The result of SDS-page.