Core of APOllO E.Cotector: Customization

By utilizing the concept of co-transformation, APOllO can offer various E.Cotectors with scFv, color signal or GBP and even any desired combination. Therefore, APOllO could customize the E.Cotector to satisfy the need of various detection platforms.

Figure 1. With the co-transform technique, we can insert any scFv or signal-related genetic sequences into the E.coli, and create a customized platform ─ the APOllO E.Cotector.

Single Chain Variable Fragment

Probe: scFv from targeted drugs

In order to provide doctors with new, direct, and innovative methods in determining the usage of monoclonal-antibody-targeted drugs, we redesigned the FDA approved monoclonal antibody targeted drugs, such as Bevacizumab (Avastin® anti-VEGF) ^[1], Cetuximab (Erbitux® anti-EGFR) ^[2] and Trastuzumab (Herceptin® anti-HER2) ^[3] into scFv as probes.

Figure 2. We design the platform to detect multimarkers as the reference for applying the combination therapy.

Each distinct scFv of targeted drugs is displayed on the surfaces of E.coli allowing it to specifically detect target molecules.

Furthermore, since APOllO E.Cotector expresses scFv and color signals at the same time, the specific molecules that correspond to the scFv can be identified by different colors, which allows for an accurate prescription of monoclonal antibody targeted drugs.

Figure 3. E.Cotector

Transmembrane Protein of scFv

To display scFv on the surface of E.coli, we use a transmembrane protein. The transmembrane protein is composed of lipoprotein (Lpp) and outer membrane protein A (OmpA).

Figure 4. Transmembrane protein: Lpp-OmpA is composed of lipoprotein (Lpp) and outer membrane protein A (OmpA).

Lpp-OmpA was designed as a fusion protein consisting of the signal sequence and first 9 amino acids of Lpp, residue 46~159 amino acids of OmpA. The Lpp of the N-terminal of this fusion protein targets the protein on the membrane while the transmembrane domain of OmpA serves as an anchor. Owing to the fact that it is on the external exposed loops of the C-terminal of OmpA, scFv can be easily anchored to the outer membrane. Between the OmpA and scFv, there is a cut site of restriction enzyme called NcoI allowing for the linked scFv to be easily changed (like a cassette) ^[4].

Figure 5. To change the scFv sequence easily, we designed the NcoI restriction site between Lpp-OmpA and scFv. When designing XbaI-SpeI restriction site between Lpp-OmpA and scFv, it can cause a mixed site. Therefore, the NcoI restriction site rather than the EX-SP restriction site was designed.

Color Signal

The color signals that we have selected are fluorescent proteins and chromoproteins. Cooperating with iGEM, all of the resources that were from the giant registry of iGEM is accessible to every iGEMer. APOllO utilized the red flourescent protein BBa_E1010, the green fluorescent protein BBa_E0040, and the blue chromoprotein BBa_K592009.

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Figure 6. Different Color Signal

Gold Binding Polypeptide

Another plasmid is gold binding polypeptide, abbreviated as GBP. APOllO may display GBP on the surface of E.coli for binding on gold surface.

GBP was designed with the three-repeated following 14 amino acids sequences: [MHGKTQATSGTIQS]. The binding sequence of GBP does not contain cysteine which can form a covalent thiol linkage with gold, the linkage to the gold surface in Self-Assembled Monolayers (SAMs)^[5].

The mechanism of the connection between GBP and gold metal plane remains unknown. By using Molecular Dynamics (MD), it indicates that GBP, with an antiparallel β-sheet structure, can recognize gold surface via OH-binding. It is likely that the hydroxyl, together with amine, ligands on GBP recognize the atomic lattice of gold, aligning the molecule along the variants of a six-fold axis on the Au (111) surface ^[6].

Figure 7. GBP can recognize and bind on the gold surface.

Transmembrane Protein of GBP

To display the GBP to the outer membrane of E.Cotector, we use a transmembrane protein called Long-chain fatty acid short as FadL. We selected the first 384 amino acids sequence from the FadL for the transmembrane protein of GBP^[7].

Figure 8. Transmembrane Protein FadL transports GBP out of the surface of E.coli.

Application: Immobilize on Gold

According to the concept of biosensor, APOllO’s customers may deem the E.Cotector to play the role of biological recognition part and the gold chip to act as the signal transducer part. Combining with multiple physicochemical nanoscale detectors in various fields, such as optical, electrochemistry, microbalance and etcetera, greater precision and accuracy will be achieved.

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Figure 9. Concept of Biosensor via E.Cotector