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Phospholipid bilayer surface configuration probed quantitatively by (31)P field-cycling NMR.

ABSTRACT: (31)P relaxation of the diester phosphate of phospholipids in unilamellar vesicles has been studied from 0.004 to 11.7 T. Relaxation at very low fields, below 0.1 T, shows a rate increase that reflects a residual dipolar interaction with neighboring protons, probably dominated by the glycerol C3 protons. This interaction is not fully averaged by faster motion such as rotational diffusion perpendicular to the membrane surface. The remaining dipolar interaction, modulated by overall rotational diffusion of the vesicle and lateral diffusion of the lipid molecules, is responsible for the very low-field relaxation. These measurements yield a good estimate of the time-average angle between the membrane surface and the vector connecting the phosphorus to the glycerol C3 protons, based on the classic theory by Woessner. Dynamic information is also obtained. Implications for solid-state NMR and other studies are discussed.

SUBMITTER: Roberts MF

PROVIDER: S-EPMC535391 | biostudies-literature | 2004 Dec

REPOSITORIES: biostudies-literature

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Phospholipid bilayer surface configuration probed quantitatively by (31)P field-cycling NMR.

Roberts Mary F MF Redfield Alfred G AG

Proceedings of the National Academy of Sciences of the United States of America 20041129 49

(31)P relaxation of the diester phosphate of phospholipids in unilamellar vesicles has been studied from 0.004 to 11.7 T. Relaxation at very low fields, below 0.1 T, shows a rate increase that reflects a residual dipolar interaction with neighboring protons, probably dominated by the glycerol C3 protons. This interaction is not fully averaged by faster motion such as rotational diffusion perpendicular to the membrane surface. The remaining dipolar interaction, modulated by overall rotational dif ...[more]

PMID: 15569928

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Project description:Exchange dynamics between molecules free in solution and bound to the surface of a large supramolecular structure, a polymer, a membrane or solid support are important in many phenomena in biology and materials science. Here we present a novel and generally applicable solution NMR technique, known as dark-state exchange saturation transfer (DEST), to probe such exchange phenomena with atomic resolution. This is illustrated by the exchange reaction between amyloid-? (A?) monomers and polydisperse, NMR-invisible ('dark') protofibrils, a process of significant interest because the accumulation of toxic, aggregated forms of A?, from small oligomers to very large assemblies, has been implicated in the aetiology of Alzheimer's disease. The (15)N-DEST experiment imprints with single-residue-resolution dynamic information on the protofibril-bound species in the form of (15)N transverse relaxation rates ((15)N-R(2)) and exchange kinetics between monomers and protofibrils onto the easily observed two-dimensional (1)H-(15)N correlation spectrum of the monomer. The exchanging species on the protofibril surface comprise an ensemble of sparsely populated states where each residue is either tethered to (through other residues) or in direct contact with the surface. The first eight residues exist predominantly in a mobile tethered state, whereas the largely hydrophobic central region and part of the carboxy (C)-terminal hydrophobic region are in direct contact with the protofibril surface for a significant proportion of the time. The C-terminal residues of both A?40 and A?42 display lower affinity for the protofibril surface, indicating that they are likely to be surface exposed rather than buried as in structures of A? fibrils, and might therefore comprise the critical nucleus for fibril formation. The values, however, are significantly larger for the C-terminal residues of A?42 than A?40, which might explain the former's higher propensity for rapid aggregation and fibril formation.

Dataset Information

Phospholipid bilayer surface configuration probed quantitatively by (31)P field-cycling NMR.

Publications

Phospholipid bilayer surface configuration probed quantitatively by (31)P field-cycling NMR.

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