LIPOPARTICLE TECHNOLOGY
THE LIPOPARTICLE
Lipoparticles are membrane-enveloped virus-like particles (VLPs) containing high concentrations of structurally-intact membrane proteins on their surface. The Lipoparticle represents a cell-free solution for manipulating concentrated, conformationally-intact membrane proteins.
LIPOPARTICLE STRUCTURE
The Lipoparticle structure is based on membrane-enveloped retroviruses. Retroviral virus-like particles are produced when the viral core protein 'Gag' buds through the cell membrane. The core becomes enwrapped by the membrane and the VLP is then free to diffuse into the external medium. Integral Molecular creates VLPs containing specific cellular membrane proteins for use as biochemical tools to study GPCRs, ion channels, and other membrane proteins. The Lipoparticle has been engineered to be completely disabled and non-infectious.
LIPOPARTICLE PRODUCTION
To produce Lipoparticles, cells are induced to simultaneously express 1) high levels of a desired membrane protein and 2) the retroviral Gag core protein. As each virus core buds out of a producer cell, it is surrounded by cell membrane containing the target membrane protein. By harvesting Lipoparticles at peak levels of membrane protein expression, membrane proteins can be captured in a stable format at their highest expression levels.
LIPOPARTICLE COMPOSITION
Lipoparticles are similar in composition to retroviruses, which contain about 60% protein, 15% phospholipid, 15% cholesterol, and 10% other materials by weight. Each Lipoparticle contains 50-200 molecules of the membrane protein of interest, comparable to the number of viral Envelope proteins naturally packaged onto infectious retroviruses. Final concentrations of typical Lipoparticle preparations are 1011 particles/ml and contain approximately 500 µg/ml total protein. When compared to cells or membrane vesicle preparations, the membrane proteins within Lipoparticles are concentrated approximately 10-100-fold based on total protein. Lipoparticles typically contain 50-200 pmol/mg of specific receptor.
ADVANTAGES
Lipoparticle offer a number of advantages compared with traditional membrane protein sources such as cells and membrane preparations:
- Lipoparticles are a source of concentrated membrane proteins.
Lipoparticles are prepared and purified to eliminate cytoplasmic proteins, mis-oriented proteins, and contaminating vesicles. Membrane proteins are captured onto Lipoparticles during peak periods of target protein expression, enabling even difficult membrane proteins to be captured at high levels.
- Lipoparticles are a convenient and consistent source of membrane protein. Lipoparticles maintain membrane proteins in their native lipid environment, preserving the proteins' orientation and conformation. Lipoparticles are stable frozen and refrigerated, thereby eliminating end-user preparation steps and reducing experimental variability.
- Lipoparticles can be used in advanced and miniaturized formats.
Lipoparticles can be used in conventional formats such as microplates, but because of their small size (~150 nm) and exceptional purity, Lipoparticles can also be adapted to instruments and formats that are otherwise difficult for membrane proteins, such as microfluidics, microarrays, beads, and biosensors.
