Difference between revisions of "Part:BBa K3853009"

Latest revision as of 08:58, 21 October 2021

his-tag-SpyTag-AAO

Aryl alcohol oxidase (AAO) is an enzyme containing flavin-adenine-dinucleotide (FAD). This is the version with SpyTag. In order to constructed our multi-enzyme complex, we introduced the SpyTag/SpyCatcher system. We added SpyTag to the N-terminus of each protein through 10 × ELP, which is a oligopeptide linker that does not affect the function of the protein it attaches to, as described in the literature^[1]. So this part can be combined with dCas9-SpyCatcher through covalent isopeptide action, thereby being immobilized on dsDNA. His-tag was added to purify the protein. We use BBa_K3853053 to construct the expression system to express and purify the protein.

Biology

Aryl alcohol oxidase (AAO, EC 1.1.3.7), a member of the glucose-methanol-choline oxidase / dehydrogenase (GMC) superfamily, is an enzyme containing flavin-adenine-dinucleotide (FAD) that catalyze the oxidation of aromatic and aliphatic allylic primary alcohols to the corresponding aldehydes while reducing molecular oxygen to H₂O₂(The mechanism has shown in Fig. 1).

Fig. 1 H₂O₂ production mechanism of AAO.

Usage

The SpyTag was fused to the N-terminus of AAO. The fusion protein could combined with dCas9-SpyCatcher (which is producted by BBa_K3853055 ) for multi-enzyme complex assembly. we obtained the composite part BBa_K3853053 (Fig. 2) and transformed the constructed plasmid into Pichia pastoris GS115 to verify its expression. The positive clones were cultivated.

Fig. 2 Gene circuit of SpyTag-AAO.

Characterization

1. Identification

The synthetic plasmid was linearized and electrotransformed into Pichia pastoris GS115. Colony PCR was applied to screen monoclonal colonies that had positive transformation results for subsequent gene sequencing verification. The target bands appeared in the normal position, and the result was shown in Fig. 3. Sequencing results ( File 1 ) showed a successful transformation.

Fig. 3 Agarose gel electrophoresis of PCR products of monoclonal colonies of SpyTag-AAO.

2. qRT-PCR

For assaying the mRNA expression level of AAO, qRT-PCRs were performed. After methanol induction for 60 h, samples containing AAO-expressing strain were taken. We did data analysis using a variation of the Livak method. To determine the relative expression level of SpyTag-AAO vs. reference gene ACT1, total RNA was extracted from samples containing equal wet weight of recombinant P.pastoris. The C_T values for SpyTag-AAO and the reference gene ACT1 were then used to calculate the fold difference:

The results were shown in Fig. 4. The gene of SpyTag-AAO was normally transcribed in the cell.

Fig. 4 RFU change curve with cycle number.

3. Enzyme Activity

Enzyme activity of AAO was determined using veratryl alcohol as substrate, and to continuously detect the formation of the product veratraldehyde (ε₃₁₀ = 9300 M^-1·cm^-1) at 310 nm ^[2] through a 96-well microplate reader. The enzyme activity test should begin immediately after preparing the reaction system. Purified SpyTag-AAO had high degrees of activity outside the living organism (Fig. 5), which proves that AAO works well.

Fig. 5 The detection of veratraldehyde reflected as the changes of A₃₁₀ in 1 min.

References

[1] Lim, S., Kim, J., Kim, Y., Xu, D. & Clark, D. S. CRISPR/Cas-directed programmable assembly of multi-enzyme complexes. Chemical communications (Cambridge, England) 56, 4950-4953, doi:10.1039/d0cc01174f (2020).

[2] Jankowski, N., Koschorreck, K. & Urlacher, V. B. High-level expression of aryl-alcohol oxidase 2 from Pleurotus eryngii in Pichia pastoris for production of fragrances and bioactive precursors. Applied microbiology and biotechnology 104, 9205-9218, doi:10.1007/s00253-020-10878-4 (2020).

Sequence and Features