Lipid Internal Dynamics Probed in Nanodiscs

Nanodiscs offer a very promising tool to incorporate membrane proteins into native-like lipid bilayers and an alternative to liposomes to maintain protein functions and protein-lipid interactions in a soluble nanoscale object. The activity of the incorporated membrane protein appears to be correlated to its dynamics in the lipid bilayer and by protein-lipid interactions. These two parameters depend on the lipid internal dynamics surrounded by the lipid-encircling discoidal scaffold protein that might differ from more unrestricted lipid bilayers observed in vesicles or cellular extracts. A solid-state NMR spectroscopy investigation of lipid internal dynamics and thermotropism in nanodiscs is reported. The gel-to-fluid phase transition is almost abolished for nanodiscs, which maintain lipid fluid properties for a large temperature range. The addition of cholesterol allows fine-tuning of the internal bilayer dynamics by increasing chain ordering. Increased site-specific order parameters along the acyl chain reflect a higher internal ordering in nanodiscs compared with liposomes at room temperature; this is induced by the scaffold protein, which restricts lipid diffusion in the nanodisc area.