Part:BBa_K1189019:Experience

Heavy ferritin subunit fused to an E coil

BBa_K1189019 is the heavy subunit of human ferritin fused to a linker E coil (BBa_K1189011), under control of a lactose inducible promoter (BBa_R0010) and a strong RBS (BBa_B0034). Twenty-four of these heavy subunits will assemble to form a protein shelled, iron sequestering nanoparticle (Chasteen et al., 1999) (see Figure 1). Ferritin is ubiquitous across prokaryotic and eukaryotic systems and is used to buffer intracellular iron by crystallizing it in its core using (Chasteen et al., 1999). The heavy chain contains ferroxidase protein domains oriented toward ferritin's to cause the oxidation of intracellular iron from Fe^2+ to Fe^3+ and initiate formation of a ferrihydrite core. (Chasteen et al., 1999). These nanoparticles are robust, remain stable at extreme pHs, withstand temperature variations, and can be used as a protein scaffold (Kim et al., 2011)

Figure 1. Ribbon visualization of a fully assembled ferritin protein.

Design features

BBa_K1189019 has an N-terminal fusion to an E coil connected to ferritin by a GS linker (Figure 2).

Figure 2. E coil fused via a GS linker to the heavy ferritin subunit under control of the LacI inducible promoter and a strong RBS. This construct will for a spherical nanoparticle which can bind up to 24 proteins of interest assuming they are expressed in fusion with the complementary K coil.

The coil system is of utility to other iGEM teams because they can express K coils on their own proteins of interest, and bind them to the complementary E coil on ferritin. Such a coiled-coil linker system reduces potential for large protein fusions to harm ferritin formation, allowing users to build intricate nanoparticle devices with myriad proteins. See Figures 3 application examples.

Figure 3. Using the E and K coils in combination with ferritin as a scaffold system allows the creation of brand new FerriTALEs or protein scaffolds.

This heavy ferritin chain was inpsired by human heavy ferritin (P02794 [UniParc]), codon optimized for E. coli K12, and commercially synthesized as shown in Figure 2. The iGEM Calgary team switched this construct into pSB1C3.

Results

The 2013 iGEM Calgary team did not make use of this sequence per se. Rather, they replicated this sequence using PCR, and integrated it into other constructs for their final system (BBa_K1189018, BBa_K1189021, and BBa_K1189037). Please see these respective pages for characterization data of these respective systems.

References

Chasteen, N. D., & Harrison, P. M. (1999). Mineralization in ferritin: an efficient means of iron storage. Journal of structural biology, 126(3), 182-194.

Dehal, P. K., Livingston, C. F., Dunn, C. G., Buick, R., Luxton, R., & Pritchard, D. J. (2010). Magnetizable antibody-like proteins. Biotechnology journal, 5(6), 596-604.

Kim, S. E., Ahn, K. Y., Park, J. S., Kim, K. R., Lee, K. E., Han, S. S., & Lee, J. (2011). Fluorescent ferritin nanoparticles and application to the aptamer sensor. Analytical chemistry, 83(15), 5834-5843.

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