Difference between revisions of "Part:BBa K3117029"

Revision as of 18:07, 21 October 2019

scFv bispecific antibody against GPA33 and CD3 codon optimized for CHOs

BBa_K3117026 is a fusion protein of an anti-CD3 single-chain variable fragment (scFv) and SpyTag (BBa_K3117015).

Usage and Biology

The sequence contains a C-terminal His-tag for easy purification and detection. Secretion of the protein is ensured by an Igk leader. When the protein passes the membrane, the leader segment is cleaved off. By connecting the variable regions of the heavy and the light chain of an anti-CD3 antibody with a short GGGGS linker (BBa_K3117004), the scFv retains its antigen-binding ability and is much smaller than a conventional antibody. Thus, it is well suited as part of a fusion protein with another effector. The SpyTag attached to the scFv belongs to the SpyTag/SpyCatcher system and is one part of the FbaB protein of Streptococcus pyogenes. Once it comes into contact with its corresponding other part, the SpyCatcher (BBa_K3117016), they bind covalently. This allows our part to be used in a modular manner in combination with other molecules carrying the SpyCatcher.

Our part targets CD3 on T lymphocytes, and thereby activates them. The most prominent effect of such activation is the release of cytotoxic granula into the environment of the cell. T cells play an integral part in the immune system of the body and are e.g. tasked with the identification and destruction of aberrant cells. Anti-CD3 antibodies are therefore a major tool in cancer research and also in cancer therapy (Ellerman, 2019).

By providing a modular platform, our part can be used in combination with a large variety of effector molecules and other antibodies to further evaluate the therapeutic potential of this application.

Sequence and Features

Characterization and measurement

The construct 2b (K2b) was synthesized by IDT. It was cloned into the expression vector pSEC/tag2/Hygro\C\-\OK by Gibson Assembly. Our protein was under control of the CMV promotor ensuring a high-level constitutive expression. Afterwards, the construct was brought into HEK293T cells with either calcium phosphate transfection or lipofection.

The accuracy of the inserted DNA after cloning was confirmed with sequencing. The data is depicted in Fig. 1.

Bild Sequencing K2b Figure 1: Sequencing data of the complete K2b

Fig. 2 shows the harvest after transfection into HEK 293T cells in a western blot. For detection, the His-Tag in the K2b sequence (BBa_K3117005) provides the opportunity to be used as a target for a primary antibody in a western blot. K2b can be seen at expected height (41 kDa). Presence of K2b in the medium proves the function of the Igk leader (BBa_K3117006), which is directing the protein into the secretory pathway.

Bild Ernte Figure 2: Western blot of the harvest after transfection into HEK 293T cells with an anti-His-Tag antibody

Furthermore the His-Tag (BBa_K3117005) in K2b allows purification of the protein with HisTrap columns. The western blot after this purification is shown in Fig. 3, showing the remaining presence of the protein after this step.

Bild Aufreinigung Figure 3: Western blot of the purified protein with HisTrap columns with an anti-His_tag antibody

For the SpyTag/SpyCatcher reaction the protein K2b was added to the protein K2a (BBa_K3117026). A height of 83 kDa was expected in the afterwards performed western blot, depicted in Fig 4. A specific band appeared after adding the two products, but this band was running at ~120 kDa. This size could be explained by formation of trimeric protein (Schoene, Fierer, Bennett, & Howarth, 2014).

Bild TagCatcher Figure 4: Western blot after SpyTag/SpyCatcher reaction