Difference between revisions of "Part:BBa K3187003"

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	contrast, samples were negative-stained with uranyl acetate. We were able to show a high density of visually		contrast, samples were negative-stained with uranyl acetate. We were able to show a high density of visually
	intact VLPs all over the sample measuring a diameter of 60 nm or less (Fig. 2). For more information about VLP assembly,		intact VLPs all over the sample measuring a diameter of 60 nm or less (Fig. 2). For more information about VLP assembly,
−	visit our <a href="#"target="_blank">wiki</a>.	+	visit our <a href="https://2019.igem.org/Team:TU_Darmstadt/Project/P22_VLP"target="_blank">wiki</a>.
	<div style="text-align: center;">		<div style="text-align: center;">
	<img class="img-fluid center" src="https://2019.igem.org/wiki/images/5/52/T--TU_DARMSTADT--invitro_UZ_TEM.png" style="max-width:60%" />		<img class="img-fluid center" src="https://2019.igem.org/wiki/images/5/52/T--TU_DARMSTADT--invitro_UZ_TEM.png" style="max-width:60%" />

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Revision as of 17:39, 19 October 2019

Superfolder Green Fluorescence Protein x P22 Bacteriophage Scaffolding Protein Fusion

Profile

Name	sfGFP scaffold protein fusion protein
Base pairs	1547
Molecular weight	46.1 kDa
Origin	Enterobacteria phage P22; Aequorea victoria
Parts	T7-Promoter, lac-operator, RBS(g10 leader sequence), sfGFP, Strep-tag II, scaffold protein (SP), double terminator (rrnB T1 terminator and T7Te terminator)
Properties	P22 capsid assembly; loading the capsid with sfGFP

Usage and Biology

This protein is a fusion protein consisting of the GFP variant sfGFP (superfolder GFP) and the scaffold protein from Enterobacteria phage P22, which is one of the two proteins needed for the assembly of the virus capsid ^{[1] [2]} . By fusing these two proteins we can load our VLPs with sfGFP ^[3] . In between those two proteins is a Strep-tag II for protein purification.
The protein expression is induced with isopropyl β-d-1-thiogalactopyranoside, starting the expression of the T7 polymerase in E. coli BL21(DE3), that binds to the T7 promoter and removing the repressor from the lac-operator.

Methods

Cloning

The fusion protein was cloned into the pACYCT2 backbone with Gibson Assembly. To verify the cloning, the sequence was controlled by sanger sequencing by Microsynth Seqlab.

Purification

The protein was heterologously expressed in E. coli BL21 and purified with GE Healthcare ÄKTA FPLC. The used affinity tag was Strep-tag II.

SDS-Page and Western blot

To verify that the CP-LPETGG was produced, a SDS-Page followed by a Western blot was performed.

Assembly

The assembly is tested in vivo and in vitro. The assembled VLPs are collected with ultracentrifugation and are visualized with TEM.

Results

Cloning and Expression

The successful cloning was proven with sanger sequencing and production with a Western blot.

Fig. 1 shows that SP has a molecular weight of approximatley 45 kDa. This is about the expected size of 46.1 kDa. Two additional bands in this lane can be observed. One at est. 25 kDa and one between 25 and 37 kDa. The lower band may be sfGFP and upper band scaffold protein. We came to this conclusion by comparing the lane of Sp-sfGFP with lanes of only SP and with sfGFP with TEV cleavage site. Those two bands are probably produced by the denaturing of the SP-sfGFP fusion protein. During denaturation for SDS-PAGE sample preparation, the fusion protein can break in two parts, sometimes it breaks in front and sometimes after the Strep-tag. This is indicated by the fact that both bands are stained by an anti strep-tag western blot. The band of Strep-tag and SP can be observed at a size of est. 30 kDa. This is larger than the expected, theoretical size of SP at about 18 kDa. Because the plasmid used for expression was verified by sequencing before, and the fusion protein has the right size when it is not broken from sample preparation, we suspect that the protein is the right one and it just behaves unexpected in this SDS PAGE.

Assembly

The images of ultracentrifugation displays that monomeric proteins were separated from assembled capsids by ultracentrifugation at 150.000 x g in a sucrose cushion (35% w/v). After completion of the ultracentrifugation treatment, sediment was clearly visible in the centrifuge tube which we suspected to mainly contain VLPs. Transmission electron microscopy (TEM) was used to image capsids taken from the sediment. For increased contrast, samples were negative-stained with uranyl acetate. We were able to show a high density of visually intact VLPs all over the sample measuring a diameter of 60 nm or less (Fig. 2). For more information about VLP assembly, visit our wiki.

The image shows assembled VLPs. The green flourescence of the VLP pellet indictes that we succesfully loaded our VLPs with sfGFP by using our sfGFP-SP fusion protein.

References

1. ↑ W. Earnshaw, S. Casjens, S. C. Harrison, Assembly of the head of bacteriophage P22: X-ray diffraction from heads, proheads and related structures J. Mol. Biol. 1976, 104, 387. [1]
2. ↑ W. Jiang, Z. Li, Z. Zhang, M. L. Baker, P. E. Prevelige, W. Chiu, Coat protein fold and maturation transition of bacteriophage P22 seen at subnanometer resolutions, Nat. Struct. Biol. 2003, 10, 131. [2]
3. ↑ Dustin P. Patterson, Benjamin Schwarz, Ryan S. Waters, Tomas Gedeon, and Trevor Douglas, Encapsulation of an Enzyme Cascade within the Bacteriophage P22 Virus-Like Particle ,ACS Chemical Biology 2014 9 (2), 359-365 [3]

Sequence and Features