Coding

Part:BBa_K1123016

Designed by: Ardjan van der Linden   Group: iGEM13_TU-Eindhoven   (2013-08-31)
Revision as of 14:23, 4 October 2013 by ArdjanvanderLinden (Talk | contribs)

DNA Coding Sequence for 1G70 Protein

This part contains the DNA sequence for the 1G70 protein. It can be placed behind any promoter of your choice and expressed with ease. Within the scope of our project this protein was expressed due to its high Arginine and Lysine concentration. This could then be used to provide CEST contrast within an MRI.

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 NgoMIV site found at 64
    Illegal NgoMIV site found at 148
    Illegal NgoMIV site found at 232
    Illegal NgoMIV site found at 316
  • 1000
    COMPATIBLE WITH RFC[1000]

Characterization

Characterization by the TU Eindhoven 2013 iGEM Team

This part was designed to generate CEST MRI contrast. The basic principle behind this technique is based on compounds that contain pools of exchangeable protons that can be selectively saturated using radiofrequency irradiation. Upon proton exchange with bulk water, these compounds can be indirectly visualized by measuring the bulk water using an MRI machine. The amino acids Lysine, Arginine, Threonine and Serine contain those exchangeable protons and polypeptides containing those amino acids in abundance are therefore potential contrast agents (see also [http://2013.igem.org/Team:TU-Eindhoven/Background CEST 101]).

The protein of this part has a Arginine percentage of 46 %, which is high compared to other (native) proteins. Therefore, it was expected that this protein would be detectable using CEST MRI.

Methods

The proteins were (aerobically) overexpressed in BL21 using a pET28a vector with a T7 promotor. The bacteria were spun down and fixed in PFA. The entire pellet (bacteria containing our proteins) was then measured in a 7 T Bruker MRI machine. First, the correct water frequency was determined, the machine was shimmed, i.e. a homogeneous magnetic field was created. The first measurement was a T2 weighed image for general orientation. Subsequently local shimming was performed on each of the separate pellets. For the final measurements, the saturation pulse was set to vary from ca. -4ppm to ca. +4ppm (relative to water), the measurements were averaged over 8 separate scans. Also a S0 (without saturation pulse) image was taken.

Results

This data was processed resulting in a asymmetry plot (MTR_assymetric) and a contrast plot visualizing the difference of the sample with the control sample. This was done by both subtracting (absolute difference) and dividing (relative difference). For a complete overview of the processing steps see the TU-Eindhoven 2013 [http://2013.igem.org/Team:TU-Eindhoven/MRIProcessing MRI Data Processing page]. The results are shown below: TU-Eindhoven Parts MRI 1G70.png

Conclusion

Around 2.0 ppm there seems to be a small arginine peak in the MTR_assymetric plot. But when compared to the control sample there was no detectable difference and therefore no CEST contrast.


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