Difference between revisions of "Part:BBa K3823001"

Revision as of 11:45, 19 October 2021

SQR(Sulfide: Quinone Oxidoreductase) from Acidithiobacillus spp.

Brief introduction

Sulfide: quinone oxidoreductase (SQR), is an ancient flavoprotein of the disulfide oxidoreductase family that is present in nearly all domains of life. It can oxidize sulfide to zero-valent sulfur. SQRs were first found in sulfide trophic bacteria, later SQR-like enzymes were found in the mitochondria of some fungi, as well as in all animal species whose genomes have been sequenced. Several SQRs have been purified and characterized by biochemical methods. They are considered to be integral monotopic membrane proteins, associating with the membrane through amphipathic helices. The monomeric molecular mass of the enzyme is around 50 kDa. The enzyme usually harbors a covalently-bound FAD cofactor in each monomer. However, FAD can also be non-covalently bound as in the SQR of A. ferrooxidans and some other organisms.

Characterization

1.The mRNA expression level of the target gene was detected by RT-qPCR
We extracted RNA of our engineered bacteria and wild-type bacteria for RT qPCR experiment. The relative content of target mRNA in each group was calculated based on 16s gene of E.coli. The experimental results can prove that our engineering bacteria can transcribe the mRNA of the introduced gene normally. (There is no target gene in the wild type, the relative expression of engineering bacteria is very high and the difference is large)

Result of RT-qPCR for four genes

2.The expression level of the target protein was detected by SDS-PAGE
We first tried to introduce plasmids linked with 1/2/3/4 target genes into E.coli DH5α, and detected their protein expression levels. However, due to the low expression amount and the limitation of Spectrophotometry, we did not find significant differences between the engineered strain and the wild type protein strips.

SDS-PAGE bands of four genes regulated by the promoter of J23110

Therefore, four target genes were added with efficient T7 promoter respectively and introduced into E.coli BL21(DE3).Under the condition of IPTG induction, all proteins of strain containing target genes and wild-type strain were extracted. SDS-PAGE experiment and Coomassie brilliant blue staining showed that the expression of each target protein could be realized in E.coli BL21(DE3).

SDS-PAGE bands of four genes regulated by T7 promoter

We had hoped to construct plasmids with T7 promoter for all four genes, and then test the protein expression, but the construction process was very difficult. Finally, due to the limited time, we connected the four genes, but only the SQR gene was regulated by the T7 promoter. In the staining results, only the SQR band was obvious, but it was speculated that the other proteins should be able to express normally.

SDS-PAGE bands of T7-SQR-J23110-SDO-APR-SAT

Protein function verification experiment

In view of the the limiting capacity of our laboratory to detect the intermediates in the sulfide oxidation pathway, we mainly verified the function of our engineered bacteria from the oxidation level of sulfide and the generation level of sulfate.
Characterization experiment of S^2- oxidation amount
We configured a series of sodium sulfide solutions with concentration gradient and tested them with detection reagents according to certain methods. The standard curve obtained is ideal. It can be considered that our detection method can accurately reflect the relative content of sulfide in the solution within this concentration range.

stander curve of S^2-

We put the engineered bacteria and wild-type bacteria into a certain concentration of sodium sulfide solution, take out the bacterial solution every 30 min to detect the residual sulfide concentration. The results show that our engineered bacteria can oxidize sulfide better. (because the bacteria have a certain adsorption effect on sulfide, the initial sulfur ion concentration of the two groups of added bacterial solution is lower than blank)

concentration of S^2- in liquid environment with different bacteria
SSAS: pET3a-T7-SQR-J23110-SDO-APR-SAT WT: wide type BK: blank

Sequence and Features