Difference between revisions of "Part:BBa K3089026"

Latest revision as of 15:11, 21 October 2019

T7 promoter+rBalcp19K-linker-mfp5-His

This composite part is meant to express rBalcp19k-linker-mfp5 fusion genes under T7 promoter, and 7XHis-tag was fused on the C terminal to achieve affinity protein purification. This composite part is also expressed in Pichia pastoris( BBa_K3089017)after codon optimization, and is an updated version from the basic part rBalcp19k( BBa_K3089008) which is expressed in Pichia pastoris as well. Mfp5 is the mussel foot protein from Mytilus galloprovincialis responsible for interface adhesion. rBalcp19k, the barnacle adhesive protein from Balanus albicostatus, its homologous gene serves as adhesive proteins, also playing the role of interfacial adhesion in a way that mfp5 does in mussels(Figure 1.) We linked them together to achieve better adhesive ability, because rBalcp19k can self-assemble into aggregated nanofibers at acidic pHs. This composite part would be a promising new generation of bio-inspired adhesives for a wide range of applications.

Characterisation

Three different experiments were done to characterise the BBa_K3089026 biobrick:

• protein expression
• protein purification
• 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 3), 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 Figure 4, 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.