Elliptical Structure of Phospholipid Bilayer Nanodiscs Encapsulated by Scaffold Proteins: Casting the Roles of the Lipids and the Protein

Abstract

Phospholipid bilayers host and support the function of membrane proteins and may be stabilized in disk-like nano structures allowing for unprecedented solution studies of assembly, structure and function of membrane proteins. Based on small-angle neutron scattering in combination with variable temperature studies of synchrotron small-angle x-ray scattering on nanodiscs1 in solution we show that the fundamental nanodisc unit, consisting of a lipid bilayer surrounded by amphiphilic scaffold proteins, posses intrinsically an elliptical shape. The temperature dependence of the curvature of the nanodiscs prepared with two different phospholipid types (DLPC and POPC) shows that it is the scaffold protein that determines the overall elliptical shape and that the nanodiscs become more circular with increasing temperature. Our data also show that the hydrophobic bilayer thickness is to a large extent dictated by the scaffolding protein and adjusted to minimize the hydrophobic mismatch between protein and phospholipid. Our conclusions result from a new comprehensive and molecular based model of the nanodisc structure and the use of this to analyze the experimental scattering profile from nanodiscs. The model paves the way for future detailed structural studies of functional membrane proteins encapsulated in nanodiscs.

Monitoring Shifts in the Conformation Equilibrium of the Membrane Protein Cytochrome P450 Reductase (POR) in Nanodiscs

“…So far, various membrane proteins were reconstituted into nanodiscs (3)(4)(5). Due to their monodispersity, small angle x-ray (SAXS) and neutron scattering (SANS) could be used to confirm, not only the size and the disc-like bilayer structure of the nanodiscs (2,6) but also the physical properties of the bilayer patch (7,8). However, attempts to structurally characterize membrane proteins in nanodiscs are currently limited to SAXS studies of bacteriorhodopsin (9) and a human cytochrome P450 (CYP3A4) (10).…”

Analysis of small-angle scattering data using model fitting and Bayesian regularization

“…The first sample contained nanodiscs of 1,2-dilauroyl-snglycero-3-phoshocholine (DLPC) and the membrane scaffolding protein MSP1D1, measured at 293 K. The data set was previously obtained and analyzed by Skar-Gislinge et al (2010). The nanodisc is a composite particle consisting of a phospholipid bilayer surrounded by two amphipathic and -helical scaffolding proteins that form a stabilizing belt around the hydrophobic edge of the bilayer (Fig.…”

Cover Feature: Lipid Internal Dynamics Probed in Nanodiscs (ChemPhysChem 19/2017)

“…[9,24,25] The lipid compositioni sa lso tuneable because it is possible to add cholesterol and/or chargedl ipids. [17] Lipid physicalp roperties in nanodiscs have been studied and compared with existing membrane models by different biophysical techniques, such as small-angle X-ray scattering (SAXS), [9,10,35,40] small-angle neutrons cattering (SANS), [35,41] NMR spectroscopy [31,34] or fluorescences pectroscopy. [35,39] Although ag eneral consensus concerning the driving force of nanodisca ssembly and the resulting MSP architecture exists nowadays, [5,11] little is known about the internal dynamics of lipids and membrane proteins embedded in nanodiscs, as well as how the lipid-lipid and lipid-protein dynamic interplay influence the membrane protein activity.Adecrease of membrane fluidity along the acyl chain for nanodiscs relative to that of artificial vesicles was indirectly measured by incorporating fluorescent probesi nto lipid preparation.…”