Part:BBa_K2916024

Expression of LeuRS in E.coli

This part is used for expression of Leucyl-tRNA synthetase needed for the OnePot PURE cell-free system.

Usage and Biology

Used in OnePot PURE

Expression and purification of LeuRS

LeuRS is one of the proteins we used for the OnePot PURE cell-free system. We expressed it in BL21(DE3) E.coli strain using a pET21a vector. The expression system has a T7 promoter, a lac operator, RBS and a T7 Terminator, enabling us to regulate the expression with IPTG.

Methods

LeuRS was purified using our protocol . To test if the protein was actually expressed, we performed a SDS-PAGE that is presented below. On the left side we can see the results included in the initial OnePot PURE paper (Lavickova et al, 2019) while on the right (batch1_a,b and batch2_a,b) are the solutions we produced ourselves. (The procedure we followed and the conditions of the experiment can be found here).

Figure 1: SDS-PAGE of OnePot PURE protein solution.

Conclusion
LeuRS has a molecular weight of around 97kDa, but even though we cannot be absolutely sure if the band shown is only due to it, we may assume that it is expressed. To verify the existence and functionality of this protein we need to proceed with more experiments that would be mainly focused on the efficiency of the system.

OnePot PURE functionality test

To make sure that we have all the proteins in our OnePot PURE protein solution, and that they all function properly we need check if proteins can be expressed in our OnePot PURE cell-free system.

Methods

We expressed superfolding GFP following the protocol we designed in 10μl reactions, and measured the fluorescence on a plate reader at excitation wavelength of 535nm. We tested the expression using different concentrations of the sf GFP DNA template and also compared it with the fluorescence produced in PURExpress from NEB.

Figure 2: sf GFP expression using 10nM DNA template.

Figure 3: sf GFP expression using 5nM DNA template.

Figure 4: sf GFP expression using 2.5nM DNA template.

Figure 5: Comparison between OnePot PURE and PURExpress at saturation.

Conclusion
The expression was successful so we can confirm that LeuRS exists in our protein solution and is also functioning properly.

Sequence and Features

Assembly Compatibility:

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

  Illegal NheI site found at 2726
  
• 21
  INCOMPATIBLE WITH RFC[21]

  Illegal BglII site found at 1198
  Illegal XhoI site found at 2675
  
• 23
  COMPATIBLE WITH RFC[23]
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal AgeI site found at 1165
  
• 1000
  COMPATIBLE WITH RFC[1000]