Part:BBa_J18932

mCherry RFP

Red fluorescent protein derived from DsRed.

Advantages:

• fast folding and maturation
• bright and photo-stable

Purity issues (update):

• Ajo-Franklin...Silver (2007) report multiple bands for mCherry purifications in E. coli
• Contains a hidden translation start site in the N-terminal -> up to 50% of protein produced in E.coli will be truncated (R. Grünberg, unpublished)
• SDS treatment and boiling before PAGE hydrolyzes the chromophore at F//MYG splitting the protein in half (discussed in Gross et al. (2000) The structure of the chromophore within DsRed protein from coral.)
• Best maturation for expression at 20 or 25 C (rather than 37)

Characterization

Expression with <a href=https://parts.igem.org/wiki/index.php?title=Part:BBa_K2319009>BBa_K2319009</a>

The protein was expressed under T7 promoter in E.coli BL21(DE3) with 6x-His tag at the N-terminal. The culture was induced at 37°C for three hours with a final IPTG concentration of 500μM. The cells were then lysed to obtain the protein. The size of the complete protein with 6x-Histag is about 26kDa. We observed two bands in the induced sample between 25 kDa and 32 kDa. The heavier band is the non-truncated protein and the lighter one is its truncated counterpart.

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   <figcaption>SDS PAGE with the cell lysate for WT uninduced, WT induced, K2319009 uninduced, K2319009 induced. The top band is the non-truncated protein and the the bottom band is the truncated protein.</figcaption>

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Purification using Ni-NTA with <a href=https://parts.igem.org/wiki/index.php?title=Part:BBa_K2319009>BBa_K2319009</a>

The cell lysate thus obtained was purified using Ni-NTA beads which only bind to proteins with a 6x-His tag, which is absent in the truncated protein. Ideally, the supernatant after binding should have the truncated protein and the elution after purification should have the non-truncated protein. This however is not true because the binding of 6xHis to Ni-NTA is not perfect.

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   <figcaption>SDS PAGE of fractions from Ni-NTA purification. The top band is the non-truncated protein and the bottom band is the protein truncated at the internal start codon (see arrowheads).</figcaption>

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Fluoroscence

Excitation Spectrum

The excitation spectrum of the purified sample (elution) was obtained at a fixed emission wavelength of 610 nm. The excitation maxima was obtained at 576 nm.

Emission Spectrum

The emission spectrum of the purified sample (elution) was obtained at a fixed excitation wavelength of 587 nm. The emission maxima was obtained at 607 nm

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<figcaption>Tht excitation and emission spectra of mCherry after normalizing it with WT BL21 (DE3) lysate.

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       Note: The kinks in the graph are an artifact of the normalization procedure to eliminate source fluoroscence.
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Quantification of Truncation

The truncation of mCherry was determined by through two different methods:

• By analysing the intensity of the truncated and non-truncated protein bands after SDS PAGE.
• By combining the fluorescence and gel intensity data of the Ni-NTA purification fractions (supernatant after binding, wash and elution).This is done assuming that truncated and non-truncated protein has the same fluorescence. The fluorescence of each of the above fractions was divided into fluorescence due to truncated and non-truncated protein based on their corresponding band intensities. The sum of fluorescence values of truncated and non-truncated protein were then used as a measure of their concentration to determine truncation.

Truncation Data

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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
  COMPATIBLE WITH RFC[1000]