Difference between revisions of "Part:BBa K2609007"

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	<img src="https://static.igem.org/mediawiki/parts/f/fc/T--IISc-Bangalore--mcp1Purification.png" width=100% style="border: 1px solid black;"></img>		<img src="https://static.igem.org/mediawiki/parts/f/fc/T--IISc-Bangalore--mcp1Purification.png" width=100% style="border: 1px solid black;"></img>
−	<figcaption>Cell pellet from BL21 (DE3) after expression (25°C, 250uM IPTG, 16hrs) in <a href="https://parts.igem.org/Part:BBa_K2609007">BBa_K2609007</a> was solubilized in different different detergents. Lane 1 and 2: Cell pellet; Lane 3: Ladder; Lane 4 and 5: Lysis buffer with no detergent; Lane 6 and 7: Lysis buffer with 1% Triton X-100; Lane 8 and 9: Lysis buffer with 2% SDS.</figcaption>	+	<figcaption>Purification from BL21(DE3) after expression (25°C, 250uM IPTG, 16hrs) in <a href="https://parts.igem.org/Part:BBa_K2609007">BBa_K2609007</a>. The cell pellet was solubilized in 8M urea before Ni-NTA purification. Lane 1:Ladder; Lane 2:Uninduced Cell Pellet; Lane 3:Induced Cell pellet; Lane 4:Ni-NTA Wash; 5: Ni-NTA Elution.</figcaption>
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	<h3>Purification and refolding with <a href="https://parts.igem.org/Part:BBa_K2609007">BBa_K2609007</a></h3>		<h3>Purification and refolding with <a href="https://parts.igem.org/Part:BBa_K2609007">BBa_K2609007</a></h3>

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Revision as of 18:05, 17 October 2018

mcp-1 under T7 expression system

This part generates Mcp-1 (a mouse monocyte chemokine) when expressed inside a T7 expression strain like BL21 (DE3). The protein is fused to a 6xHis tag and a TEV protease cleavage site at the N-term. Mcp-1 is a member of CC chemokine family that uses the CCR2 receptor for chemo-attracting monocytes to the site of release. This coding sequence lacks the heavily glycosylated C-terminus present in the wild-type protein and has been shown to have a increased chemotactic potency^[1][2]. The protein can be expressed recombinantly in a prokaryotic system because of its lack of glycosylation and post-translational modifications.

Sequence and Features

Usage and Biology

Biology

Mcp-1 belongs to the CC family of chemokines and is recognised by the CCR2 receptors found on murine monocytes. Due to its inherent homology to human CCL2, it acts as a effective chemokine for human moncytes as well. The N-term region of the protein has been implicated in receptor binding and any fusion to this terminal might result in decreased activity. In both mice and humans, the chemokine is produced by a wide variety of cell types including endothelial,fibroblasts, epithelial, smooth muscle, mesangial, astrocytic, monocytic, and microglial cells. Apart from monocytes, CCL2 has also been shown to chemoattract NK cells and T cells with comparatively lesser efficacy.^[2]

Usage

For their Phage Assisted Immune Recruitment (PAIR) system, the 2018 IISc-Bangalore iGEM team used the mcp-1 CDS fused with both N-term and C-term secretion tags (PelB and HlyA respectively) for recombination into a phage genome. This engineered phage will recruit phagocytic monocytes to the site of infection and prevent release of bacterial toxins directly into the body.

Characterization

Expression with BBa_K2609007

The protein was expressed under T7 promoter in E. coli BL21 (DE3) with a 6xHis tag connected to the N-term through a TEV protease cleavage site. Small scale induction was done at the temperatures 37°C, 25 °C and 16°C and IPTG concentrations ranging from 100uM to 1mM. The protein was found in inclusion bodies at all temperature with negligible yield at lower temperatures (See 'Solubilization'). The ideal conditions for expression after multiple trials expression were found to be the following:

• Temperature: 25°C
• IPTG Concentration: 250uM
• Time of induction: 16 hrs (Not optimized)
• Chloramphenicol concentration: 35ug/ml (Not optimized)
• Medium: LB (Not optimized)

The protein with the 6xHis and TEV protease tags should be 15.6kDa in size. Bands were seen between 17kDa and 22kDa after induction.

Solubilization with BBa_K2609007

At the favorable conditions for high yield, the protein expressed from BBa_K2609007 in a flask culture was insoluble. We postulated the formation of inclusion bodies, which are not uncommon when an eukaryotic protein is expressed in E. coli. Formation of inclusion bodies was checked by resuspension of the cell pellet in lysis buffers containing different detergents.

Small amounts of soluble protein was obtained only with 2% SDS lysis buffer. Hence, the protein forms inclusion bodies when expressed in BL21 (DE3). The absence of soluble protein was also noted at both 16°C (24 hrs, 250uM IPTG) and 37°C (3 hrs, 250uM IPTG). The inclusion from the cell pellet were solubilized in lysis buffer containing 8M urea for subsequent purification.

Purification and refolding with BBa_K2609007

After solubilization in 8M urea, the protein was directly used for a Ni-NTA purification and the purified protein (in 8M Urea) was dialysed against Tris-HCl buffer containing decreasing concentrations of urea (8M, 6M, 4M, 2M and finally 0M) for refolding. Both the solubilization and refolding protocols can be found on the IISc-Bangalore Team's protocols page.

References

[1] Yao, Yao, and Stella E. Tsirka. "Mouse monocyte chemoattractant protein 1 (MCP1) functions as a monomer." The international journal of biochemistry & cell biology 55 (2014): 51-59.

[2] Deshmane, Satish L., et al. "Monocyte chemoattractant protein-1 (MCP-1): an overview." Journal of interferon & cytokine research 29.6 (2009): 313-326.