Difference between revisions of "Part:BBa K3717005"

Revision as of 08:30, 19 October 2021

Endo-β-Galactosidase with strong promoter and RBS

Figure 1: Endo-β-galactosidase with strong promoter, RBS, and a terminator.

Construct Design

Endo-β-galactosidase an enzyme that catalyzes the cleavage of the A and B type blood antigens trisaccharides such that the remaining sugar can be classified as a H antigen, which the anti-A and anti-B antibodies are unable to recognize and thus does not elicit an immune response in the human body. Thus, the enzyme can convert both A and B blood types to universal O type. The enzyme has been previously shown to successfully convert A,B, and AB type erythrocytes to O type but lacked a cost-effective method of production.

We obtained the amino acid sequence of the endo-β-galactosidase protein, derived from Clostridium perfringens, the iGEM DNA Repository Plate (BBa_K1483001), which served as our Open Reading Frame (ORF). We attached a strong promoter and strong ribosome binding site (RBS; BBa_K880005) upstream of the open reading frame (ORF). The composite gene was synthesized through DNA cloning.

Contributions

Figure 1 - Colony PCR check for strong promoter (K88) Endo-β-Galactosidase (Part:BBa_K3717005) using VF2 and VR primers. Confirms successful ligation as a band is produced at the expected size of 2752bp, as indicated by the red triangle.

We tested protein expression of the composite part BBa_K3717005 by transforming our plasmids into BL21 E. Coli cells. We grew an overnight culture of the BL21 cells with our plasmids then diluted our cells to a standardized OD600 of ~0.1 and let it grow until an OD600 of 0.5~0.6. The diluted cultures of OD600 0.5~0.6 were then induced for expression with 0.5 M IPTG stock (to a final concentration of 0.5mM in the culture) and allowed to grow and induce overnight at room temperature.

Figure 2 - SDS Page of cell lysate for each strain: strong promoter (K88) Endo-β-Galactosidase (Endo-β-gal) (Part:BBa_K3717005). Red triangles indicate expected size for Endo-β-gal (90.8 kDa). Sequences for target proteins were found to not contain a start codon and thus have no expression, as shown by the triangles.

Our SDS-page in Fig. 2 did not show any overexpression bands for the enzymes of interest. The results indicate that there were no target proteins at their expected band sizes: 90.8 kDa band for both T7 promoter + Endo-β-gal and K88 promoter + Endo-β-gal in the induced sample. As the SDS page is of cell lysis samples, other bands present are due to innate proteins present in the bacteria cell.

Upon comparison of the amino acid sequence from Tuebingen’s parts with expected full sequences that were obtained from UniProt, we discovered that the enzyme sequences were missing the start codon (Fig. 3), which explained the non-expression of the proteins.

(figure three placeholder)

Figure 3 - Top sequence: First 59 amino acids of Team Tuebingen's 2014 Endo-β-gal part BBa_K1483001. Bottom sequence: First 60 amino acids of expected sequence for Endo-β-gal derived from Clostridium perfringens. Based on the alignment of the two sequences, Tuebingen's part is missing the first amino acid (start codon) of the Endo-β-gal protein.

Sequence and Features