Membrane Nanoparticles (MNPs)

Membrane proteins such as cell adhesion molecules (CAMs), G protein-coupled receptors (GPCRs), and ion channels are involved in a multitude of essential cellular processes. These include cell-to-cell interaction, signal transduction, and the transport of substances into and out of cells. For this reason, membrane proteins are targeted by more than half of all approved drugs. However, studying membrane proteins can be extremely challenging as their amphipathic nature makes it difficult to isolate them in a native form. Once the native conformation is lost, protein activity is compromised and certain epitopes may be altered, limiting the utility of the target protein for functional assays, antibody generation, or various other types of research. Within the past few decades, several innovative methods have been developed for isolating native membrane proteins. Included among these, membrane nanoparticles (MNPs) have been widely adopted by the scientific community for the many advantages that they can provide. Membrane nanoparticles are typically produced by over-expressing the protein of interest in a mammalian cell line, usually human embryonic kidney (HEK) cells or Chinese hamster ovary (CHO) cells to preserve correct folding and post-translational modification (PTM). Proprietary methods are then used to extract the membrane from the host cells and extrude the target protein-containing MNPs. A main advantage of using MNPs for producing membrane proteins is that the target is expressed at a high density to provide good yields and strong immunogenicity for antibody generation. In addition, the native structure and orientation of the target protein is maintained to provide more physiologically relevant experimental results. Depending on the method that is used for MNP production, further benefits include high solubility in aqueous solutions, which can simplify routine biochemical analyses, and the capacity for detergent-free purification, which allows for the use of MNPs in a broader range of downstream applications, including those involving live cells. On the flipside, a limitation of MNPs is that the target protein cannot be accurately quantified. Applications for membrane nanoparticles include enzyme-linked immunosorbent assays (ELISAs), cell-based assays, and phage display screening. MNPs are also used as immunogens for antibody generation, for chimeric antigen receptor (CAR) T cell screening, and for surface plasmon resonance (SPR) affinity analysis.