Nanodiscs as a new tool to examine lipid-protein interactions

Abstract

Nanodiscs are self-assembled discoidal fragments of lipid bilayers 8-16 nm in diameter, stabilized in solution by two amphipathic helical scaffold proteins. As stable and highly soluble membrane mimetics with controlled lipid composition and ability to add affinity tags to the scaffold protein, nanodiscs represent an attractive model system for solubilization, isolation, purification, and biophysical and biochemical studies of membrane proteins. In this chapter we overview various approaches to structural and functional studies of different classes of integral membrane proteins such as ion channels, transporters, GPCR and other receptors, membrane enzymes, and blood coagulation cascade proteins which have been incorporated into nanodiscs. We outline the advantages provided by homogeneity, ability to control oligomerization state of the target protein and lipid composition of the bilayer. Special attention is paid to the opportunities afforded by nanodisc system for the detailed studies of the role of different lipid properties and protein-lipid interactions in the functional behavior of membrane proteins.

Figure 1

Results of MD simulations of Nanodiscs assembled with DPPC molecules and scaffold protein MSP1D1 (14). Alignment of prolines shown in yellow can be seen at the left part of the top view (top), while the different conformations of the lipid acyl tails in the middle of Nanodisc and at the protein – lipid interface can be seen at the bottom.

Figure 2

Representative examples of integral membrane proteins successfully self-assembled into Nanodiscs. This include G-protein coupled receptors (29, 30, 33, 34, 53, 54), multi-subunit chemotactic receptors (48, 49, 55), complex assemblies such as the SEC translocase (40, 41, 56), many different cytochromes P450 both with and without co-incorporated reductase (, –63), human tissue factor and the enzymes of the blood coagulation cascade (–67), active trimeric bacteriorhodopsin (68) and cholera toxin binding to gangliosides (69, 70).