Part:BBa_K4088893

DnaE - C

C-terminal of Npu DnaE intein.

You can find N-terminal of Npu DnaE intein there - BBa_K4088892.

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]

Usage and Biology

Intein
Intein is a segment of a protein that can self-catalytically excised out and ligate the remaining parts of the protein (N- and C-exteins) with a peptide bond .
For this part we used the Npu DnaE intein. DnaE - alpha subunit of the DNA polymerase III intein. This intein is identified as a naturally occurring split intein in Nostoc punctiforme . Its first amino acid is cysteine which is important for protein trans-splicing to take place.

This part we used in the сomposite system - С-terminal fragment of β-lactamase fused with dCas13a and C-terminal intein (BBa_K4088890).

Improvement:NUDT_CHINA 2022

Our improvement is C-intein-t3 (Part:BBa_K4414011) a C-terminally 3 bases-truncated C-terminal of Npu DnaE intein (Part:BBa_K4088893) sequence. Intein is a segment of a protein that can self-catalytically excise out and ligate the remaining parts of the protein (N- and C-exteins) with a peptide bond. For this part, we used the Npu DnaE intein. DnaE - alpha subunit of the DNA polymerase III intein. This intein is identified as a naturally occurring split intein in Nostoc punctiforme. The improved C-intein-t3 shares a similar nucleic acid sequence to the original DnaE – C in BBa_K4088893, with only 3 bases at the c-terminus truncated. However, these differences enabled Lov2-mediated blue-light control of protein splicing.

Methods

We evaluated whether the improved C_intein can mediate the lov2-based blue light responsiveness by assaying the intein-mediated reconstitution of split-EGFP. Hence, we first fused the lov2 domain (BBa_K4016004) and the EGFP_71-239 domain on the N-terminus and the C-terminus of C_inteint3 respectively. A similar construct using the original C_intein was also constructed as a head-to-head control. Also, another plasmid expressing the fusion protein containing the N_Intein (BBa_K4088892) and the EGFP_1-70 domain was obtained.

As a head-to-head comparison, HEK-293T cells were co-transfected with the lov2-C_inteint3-EGFP_71-239 expressing and the EGFP_1-70-N_intein expressing plasmids, cells co-transfected with lov2-C_intein-EGFP_71-239 expressing and the EGFP_1-70-N_intein were used as control. Cells were either exposed to blue light (with ON [4 s]-OFF [56 s] cycles) or maintained under dark conditions since the 6th hour post-transfection. Cells were imaged or harvested for Western Blotting 48 h post-light illumination.

Results

The fluorescent imaging of the cells expressing both lov2-C_intein-EGFP_71-239 and EGFP_1-70-N_intein proteins showed strong EGFP signal in both the blue-light-illuminated group and control group kept under dark conditions. Suggesting that lov2 is not capable of inhibiting the function of the original C_intein (BBa_K4088893) under dark conditions. Intriguingly, cells expressing both EGFP_1-70-N_intein and the improved lov2-C_inteint3-EGFP_71-239 proteins showed nearly no fluorescent signal in control cells that were not illuminated by blue light, and a strong GFP signal in blue light treated group (Figure 1a). The reconstitution of EGFP was also validated via Western Blotting, which showed a significantly stronger EGFP signal in blue-light treated cells compared to the untreated cells (Figure 1b). These results demonstrated that the improvement from BBa_K4088893 to BBa_K4414011 enabled lov2-mediated light-inducible protein splicing in mammalian cells.

Figure1. Reconstitution of split-EGFP mediated by blue light-stimulated protein trans-splicing. (a) Top: the lov2-C_intein-EGFP_71-239 expressing and the EGFP_1-70-N_intein expressing plasmids in HEK-293 cells exposed in dark(left) or in blue light(right); Button: the lov2-C_inteint3-EGFP71-239 expressing and the EGFP_1-70-N_intein expressing plasmids in HEK-293 cells exposed in dark(left) or in blue light. (b) Immunoblotting of the indicated proteins in the lov2-C_inteint3-EGFP_71-239 expressing and the EGFP_1-70-N_intein expressing cells w/wo blue light treatment.