title: Optimal Bicelle Size q for Solution NMR Studies of the Protein Transmembrane Partition.
abstract: Structural characterization of transmembrane proteins in isotropic bicelles has become an increasingly popular application of solution NMR spectroscopy, as the fast-tumbling bicelles are membrane-like, yet can often yield spectral quality comparable to those of detergent micelles. While larger bicelles are closer to the true lipid bilayer, it remains unclear how large the bicelles need to be to allow accurate assessment of the protein transmembrane partition in the lipid bilayer. Here, we address the above question from the perspective of the protein residing in the bicelles, through systematic measurement of the protein chemical shift and transmembrane partition at different lipid/detergent ratios (q), ranging from 0.3 to 0.7, using the transmembrane domain of the human Fas receptor as model system. We found that the lipid environment of the bicelles, as reflected by the protein chemical shift, begins to be perturbed when q is reduced to below 0.6. We also implemented a solvent paramagnetic relaxation enhancement (PRE) approach for bicelles to show that the protein transmembrane partition in bicelles with q=0.5 and 0.7 are very similar, but at q=0.3 the solvent PRE profile is significantly different. Our data indicate that q values between 0.5 and 0.6 are a good compromise between high resolution NMR and closeness to the membrane environment, and allow accurate characterization of the protein position in the lipid bilayer.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, 02115, USA.
authors.forename: Alessandro
authors.identifier: http://orcid.org/0000-0002-5264-1980
authors.initials: A
authors.lastname: Piai
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, 02115, USA.
authors.forename: Qingshan
authors.initials: Q
authors.lastname: Fu
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, 02115, USA.
authors.forename: Jyoti
authors.initials: J
authors.lastname: Dev
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, 02115, USA.
authors.forename: James J
authors.initials: JJ
authors.lastname: Chou
mesh_terms: D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D006571:Heterocyclic Compounds / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D009942:Organometallic Compounds / Q000737:chemistry / Q000378:metabolism; D010742:Phospholipid Ethers / Q000737:chemistry; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification; D019014:fas Receptor / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: C052298:1,2-dihexadecyl-sn-glycero-3-phosphocholine; D006571:Heterocyclic Compounds; D008051:Lipid Bilayers; D009942:Organometallic Compounds; D010742:Phospholipid Ethers; D011994:Recombinant Proteins; D019014:fas Receptor; C050823:gadolinium 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetate; D004134:Dimyristoylphosphatidylcholine
keywords: NMR spectroscopy; bicelles; membrane proteins; paramagnetic relaxation enhancement; transmembrane partition