Structural Analysis of Nanoscale Self-Assembled Discoidal Lipid Bilayers
by Solid-State NMR Spectroscopy
Ying Li 1, Aleksandra Z. Kijac 1, Stephen G. Sligar 1 and Chad M Rienstra 1*
1 University of Illinois at Urbana-Champaign
* To whom correspondence should be addressed. E-mail: rienstra{at}scs.uiuc.edu.
Submitted on April 12, 2006
Revised on June 6, 2006
Accepted on 18 July 2006
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Abstract |
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Nanodiscs are an example of discoidal nano-scale self-assembled lipid/protein particles similar to nascent high-density lipoproteins (HDL) (Bayburt, T. H., Y. V. Grinkova, and S. G. Sligar. 2002. Nano Lett. 2:853-856), which reduce risk of coronary artery disease (CAD). The major protein component of HDL is human apolipoprotein A-I (apo A-I), and the corresponding protein component of Nanodiscs is membrane scaffold protein 1 (MSP1), a 200-residue lipid-binding domain of apo A-I. Here we present magic-angle spinning (MAS) solid-state NMR studies of uniformly 13C,15N-labeled MSP1 in polyethylene glycol (PEG) precipitated Nanodiscs. 2D MAS 13C-13C correlation spectra show excellent microscopic order of MSP1 in precipitated Nanodiscs. Secondary isotropic chemical shifts throughout the protein are consistent with a predominantly helical structure. Moreover, the backbone conformations of prolines derived from their 13C chemical shifts are consistent with the molecular belt model, but not the picket fence model of lipid-bound MSP1. Overall comparison of experimental spectra and 13C chemical shifts predicted from several structural models also favors the belt model. Our study thus supports the belt model of Nanodisc structure and demonstrates the utility of MAS NMR to study the structure of high molecular weight lipid-protein complexes.
Key Words:
chemical shift, high-density lipoprotein, proline, secondary structure, self-assembly, solid-state NMR
