Part:BBa_K3089006
Introduction
This part is designed for mTyr-CNK protein purification and in vitro/vivo DOPA modification of all Mfp containing recombinant proteins. The unnatural amino acid DOPA plays important role in Mfp’s adhesion. In natural Mfps came from posttranslational modification(PTM) in mussel foot cell, but E coli was unable to do so. Tyrosinases could oxidize tyrosine to turn it into DOPA. Although there is an existing tyrosinase in the part registry already, our mTyr-CNK has a higher efficiency in catalyzing relevant reactions, thus is more suitable for DOPA modification to obtain a stronger adhesion. Instead of obtaining tyrosinase from Streptomyces sp. like in most studies, ours is found in a marine archaeon Candidatus Nitropumilus koreensis.
This part was designed based on paper “A tyrosinase, mTyr-CNK, that is functionally available as a monophenol monooxygenase”(Do, Kang, Yang, Cha, & Choi, 2017).
Characterization
mTyr-CNK is well-expressed in E. coli during our experiments, and it successfully modified all of our recombinant proteins based on Mfp5 in vitro; the co-expression system where they are expressed together inside a cell for a more efficient in vivo modification also has a very interesting potential. We believe mTyr-CNK will become a very useful part for projects that involve DOPA modification. We also have various qualitative and quantitative data from protein expression, purification, and in vivo/ vitro DOPA modification. BBa_K3089006 was characterized in following experiments:
- protein expression and purification
- In vitro DOPA modification and NTB staining
- Surface coating analysis
Protein expression
The predicted size of rBalcp19k-linker-mfp5 is 28.17 kDa, and the isoelectric point is 10.41. rBalcp19k-linker-mfp5 was cloned into pET28b and expressed in E.coli BL21(DE3) Rosetta by 500μM IPTG for 5h at 37℃. In order to detect its expression, whole cells were collected after induction by centrifuging and prepared for SDS-PAGE. Results showed that no protein bands of rBalcp19k-linker-mfp5(~28 kDa) could be observed on lane rBalcp19k-mfp5 compared with lane pET28b (pET28b empty vector)(Figure 1A), which means the expression of this protein is not well in BL21(DE3) Rosetta. We can get the same results using quantitative densitometry analysis of SDS-PAGE gels (Figure 1B).
Protein purification
Barnacle cement proteins are very promising in making biomedical bio-glues. rBalcp19K from Balanus albicostatus had the properties of both self-assembly and adhesion.
It also could function in more basic condition than Mfps. Thus we also designed a novel recombinant protein by combining it with Mfp5. We expected rBalcp19k-Mfp5 would perform better adhesive ability to solidify our idea of modularisation of Mfp5.
We tried to purify it under native conditions, and we found bands of rBalcp19K-linker-mfp5 appeared between 25kDa and 35kDa on 12% SDS-PAGE gel(Figure 2), which meant it was successfully expressed and purified under native condition(see details on our methods).
Protein concentrations of rBalcp19k-linker-mfp5 were measured by BCA assay, and its yield is 1mg/L.
Surface coating analysis
After obtaining a small number of recombinant proteins, surface coating analysis for qualitatively assessing the surface adsorption ability of recombinant proteins was conducted on two of most commonly used bio-related surfaces: hydrophilic glass slides and hydrophobic polystyrene tissue culture plates. As shown in Figure3, rBalcp19k-linker-mfp5 recombinant protein showed higher surface absorption abilities on both different substrates than rBalcp19k without fusion of mfp5 on its C-terminal. It’s suggested that Mfp improves the coating ability of rBalcp19k-linker-mfp5 fusion proteins. The In-vitro DOPA modification by mTyr-CNK tyrosinase significantly improved its surface absorption abilities, which suggested the positive contribution of DOPA in adhesive protein performances.
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