Using Nanodiscs to create water-soluble transmembrane chemoreceptors inserted in lipid bilayers.

In this chapter we describe application of the emerging technology of Nanodiscs to chemoreceptors, a class of transmembrane proteins that presents many challenges to the investigator. Nanodiscs are soluble, nanoscale ( approximately 10nm diameter) particles of lipid bilayer surrounded by an annulus of amphipathic protein, the membrane scaffold protein. A transmembrane protein inserted in a Nanodisc is surrounded by a lipid bilayer much as it is prior to detergent solublization. Thus, the Nanodisc-inserted protein is in an environment that approximates its native state. Yet, that membrane protein is also water-soluble and segregated from other membrane proteins because the bilayer into which it is inserted is of very limited size and, with appropriate preparation, contains only a single protein. In a Nanodisc, the water-soluble, bilayer-inserted membrane protein can be purified by conventional techniques and analyzed for activities and interactions as a pure entity. Thus, Nanodisc technology has great promise for improving isolation, purification, and characterization of the many membrane proteins that are difficult to handle, become unstable, or lose native activity when surrounded by detergent instead of lipid bilayer. The technology has proven useful for the investigation of chemoreceptor activity as a function of oligomeric state.