Difference between revisions of "Part:BBa K5301005"

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SCSdC-mCh[1-10] is one of the components of multi-polymerized MSP.

Usage and Biology

In order to produce large nanodiscs more conveniently, we hope to flexibly extend the length of MSP according to demand, and thus propose the concept of multi-polymer MSP, which refers to large circular MSPs through end-to-end connections of multiple MSP fragments. We used NW15 as the basic MSP and selected three types of linkers (Spy/Sdy/Snoop) to achieve the connection of different MSP fragments through the formation of covalent bonds, and adopted rigorous design to prevent self-cyclization of each fragment of the multi-polymer MSP. Finally, the successful cyclization of large circular MSPs is characterized by the fluorescence of mCherry after the combination of mCherry [1-10] and mCherry [11]. SCSdC-mCh[1-10], the first component of multi-polymerized MSP, is a fusion protein composed of SpyCatcher, mCherry [1-10], NW15, and SdyCatcher, with flexible GS linkers used to connect each part.

We also utilized AlphaFold 2 to simulate the structure of SCSdC-mCh[1-10] and obtained the correct linear, non-cyclized protein conformation, as shown in the figure.

Plasmid Construction

To produce multi-polymerized MSP, we first constructed plasmids to synthesize three MSPs separately. We obtained the gene sequence of NW15 from NCBI and integrated the sequences of SpyCatcher and SdyCatcher at its N-terminus and C-terminus to form SCSdC-mCh[1-10]. We added 5' (NcoI) and 3' (XhoI) to the ends of the gene through GENEWIZ, cloning them into the vector pET-28a(+) (Kanamycin) to construct three recombinant plasmids, which were then introduced into BL21 (DE3). Subsequently, we picked multiple single colonies from the plate for colony PCR to check if the plasmids were successfully introduced into the host bacteria.

Cultivation, Purification and SDS-PAGE

Induction

We chose the T7 expression system as the pathway for protein expression and induced protein expression by adding IPTG at an appropriate time. Through experimental validation, we added the IPTG solution at a concentration of 0.8mM when the OD value of the bacterial suspension reached 0.6-0.8, resulting in substantial expression of soluble proteins.

Purification

After confirming the successful expression of SCSdC-mCh[1-10], we scaled up the culture and purified the protein. During plasmid construction, we incorporated a His-tag into the sequence, allowing for purification using nickel affinity chromatography, which specifically binds to His-tagged proteins. We eluted the protein using 300mM and 500mM imidazole, respectively, and obtained a large amount of target protein in both cases, as shown in figure 2.

Further Purification by SEC

Due to various possible reasons, the target protein obtained through nickel affinity chromatography has a relatively high concentration but still contains a significant amount of impurity proteins, which is detrimental to subsequent characterization experiments. Therefore, we chose to further purify the target protein to a higher degree of purity through SEC (Size Exclusion Chromatography). According to Figure 3, we obtained a total of six elution peaks. Through SDS-PAGE analysis of the samples corresponding to each peak, we confirmed that the purified target protein was obtained at the second and third peaks.

Structure and biological activity analysis

We attempted to incubate three protein segments in vitro through different methods to link them, and successfully obtained mCherry fluorescence images.For more information on the construction of multi-polymerized MSP, go to BBa_K5301024.

Sequence and Features