Multi-pass Transmembrane Proteins and Technology Platforms

Our Claudin18.2 has been developed with VLP and DMM/CHS platforms. Both of these versions are suitable for immunization and screening. However, the VLP version may be preferred for improved immunogenicity. For accurate affinity measurements, we recommend using the DDM/CHS version (the detergent version).

Multi-pass transmembrane proteins span the cell membrane multiple times forming multiple extracellular domains. For example, Claudin18.2, CD20, and CD133 have two extracellular loops (ECLs) with each ECL having specific functions and interactions with each other. Full length can ensure that the protein conformation is biologically relevant while enabling the ECL to be completely exposed for improved screening of ideal antibodies. As the figure below illustrates, the full length is active and relevant compared to isolated extracellular domain. It is not the case that ACRO always emphasizes full length proteins, but drug discovery R&D work needs the full-length multi-pass transmembrane proteins. Indeed, when compared, the activity of only the ECL region is worse than that of the full-length protein. ACRO is committed to providing the high quality and relevant products that meet customers' needs.

The influence of non-specific antibodies cannot be ignored. Using membrane proteins under the VLP and Nanodisc platforms may produce non-specific antibodies. Both of our platforms have corresponding isotype controls for reverse-screening and excluding non-specific antibodies. Membrane protein-VLP has an isotype control product (Cat. No. VLP-NF2P4). Membrane protein-Nanodisc has two isotype control products, one of which is MSP1D1(Cat. No. APO-H51H3) as the isotype control for tag free version. If a biotinylated membrane protein-Nanodisc is used, MSP1D1(Cat. No. APO-H81Q5) can be used as the isotype control.

Nanodisc-membrane proteins are quite different from detergent stabilized membrane proteins. First of all, in principle, Nanodisc-membrane protein are assembled on native membrane-like structures and are completely detergent free. This opens up applications like immunization use for Nanodisc assembled proteins otherwise restricted due to detergent dissolving native cell membrane and causing damage to cells. In addition, the Nanodisc version of membrane proteins are compatible with cell-based assays and CAR expression detections. The Nanodisc platform used by ACRO has been authorized by the patent holder and can be used with confidence during the development process.

Claudin18.2-VLP is tested and verified by anti-Claudin18.2 specific antibodies. The purity is evaluated by SDS-PAGE/HPLC/DLS/SEM. The conventional negative dye EM cannot see whether Claudin18.2 is on the VLP due to its low resolution. Binding activity with anti-Claudin18.2 specific antibodies can confirm the presence of Claudin18.2 on the particles.

We currently store all VLP formulated products as liquids at -70°C and ship on dry ice. We do store non- enveloped VLP products by freeze-drying. VLP immunization mainly requires attention to the choice of adjuvant dose, because VLP itself can enhance immunogenicity, which is not the case for conventional protein products.

CD24 and PD-1 are soluble proteins. They are not multi-pass transmembrane proteins, so non-enveloped VLPs are used. While multi-transmembrane proteins have hydrophobic transmembrane regions and need to be embedded on the membrane of the enveloped VLPs. The difference between VLP and enveloped VLP is whether there is a phospholipid bilayer membrane on the surface of the VLP.

If customized, the membrane protein in VLP format is expected to take 6-8 weeks.  The DDM/CHS version requires expression and purification conditions optimization of the target multi-pass transmembrane protein and detergent screening, so the development cycle is longer lasting more than 8 weeks. The customized Nanodisc version of membrane protein requires an additional 4 weeks on top of the DDM/CHS development time.