Difference between revisions of "Part:BBa K4035001"

Revision as of 08:18, 20 October 2021

CUP1 fused to Aga2 and tagged with a V5 epitope

This protein is made of the copper metallotionein CUP1 (BBa_M45090) fused to the A-agglutinin-binding subunit Aga2 (BBa_K416000) at its N-terminal and to the V5 tag at its C-terminal.

Usage and Biology

Copper metallotionein CUP1 (BBa_M45090) is a protein responsible for copper binding protein in the yeast Saccharomyces cerevisiae. Normally expressed intracellularly, CUP1 was fused to the A-agglutinin-binding subunit Aga2 (BBa_K416000) that attaches to the yeast cell wall through disulfide bonds to Aga1p. This leading to the presence of CUP1 on the outter membrane of the cell. This fusion protein also contained a V5 tag in order to check its expression by Western Blot and Immunostaining. The expression was under the control of the Gal1 promoter, so that the protein was expressed only in the presence of galactose.

Characterization

Expression of the protein in the recombinant yeast :

Figure 1 : Western Blot results

The protein expression characterization has been accomplish by two experiments, the first being a Western Blot analysis. After having transformed the EBY100 yeast with our newly formed plasmid pCTcon2V5-CUP1-V5 we tested its protein expression. For control we also tested the wild type yeast (untransformed) as well as a transformed yeast with the plasmid backbone (without insert) in two different media, one containing galactose and allowing expression and the other, lakcing galactose and thus blcking the expression. As the plasmid contains a Gal1 promoter, the system can only be expressed in the presence of galactose.

Figure 1 : The first two lines, EBY100 and pCTcon2V5 without galactose which are, respectively, wild type yeast and uninduced transformed yeast with the backbone plasmid, serve as negative controls, and show no presence of the V5 tag, as we expected. The third line, pCTcon2V5 + galactose is the induced transformed yeast with the backbone plasmid and shows expression of the V5 tag which proves that our system is expressed in the transformed yeast when induced with galactose. The fourth line is our transformed yeast with the recombinant plasmid pCTcon2-CUP1-V5 and also shows expression of the system.

We can see that we have two lines of approximately 20 to 25 kDa which is the size of the fusion protein Aga2-CUP1-V5. The smaller line could be a truncated version of the protein as we later identified a second in-frame start codon in the DNA sequence. Unfortunately the truncated version seems to be the most expressed one, corresponding to the signal intensity.

The presence of our recombinant membrane protein Aga2-CUP1-V5 in our yeast transformants is thus shown.

Figure 2a : Immunostaining of the yeast transformed with the pCTcon2-CUP1-V5 plasmid

Figure 2b : Immunostaining of the the wild type EBY100 yeast

Figure 2c : Immunostaining of the yeast transformed with backbone plasmid pCTcon2V5

Figure 2a : The blue dots represent the nuclei stained with DAPI and the green disks are the recombinant yeast cells expressing CUP1 at their surface. Due to the more intense circle we can clearly see that our system is expressed on the membrane of the protein. As these are non permeabilized cells, the antibodies bind only the extracellular proteins. We can also remark that not all the cells are expressing the system. This mainly due to...

Figure 2b : This is the negative control of the immunostaining. The blue dots are the nuclei of the cells, staining with DAPI. The green signal is background and noise.

Figure 2c : This is the positive control of the immunostaining, with the transformed yeast with the plasmid backbone pCTcon2V5 induced with galactose. We can see the cells nuclei stained with DAPI in blue and the yeast cell membranes expressing V5 tag in green.

Growth curves of the different yeast strains

In order to check if our expression system would affect the growth of our micro-organism, we performed multiple growth curves with different parameters.

Colony forming assays of the different yeast strains

A second experiment was done to check if the expression system would affect the growth of the yeast cells, a colony forming assay. That experiment consisted of counting the colonies formed by the different yeast strains, respectively wild type, backbone uninduced, backbone induced and transformant, on agar plates.

Copper absorption assays

To finally test our system we imagined an experiment to measure how muchcopper our transformed yeast could absorb.

Sequence and Features