Journal of Biomolecular NMR

, Volume 29, Issue 3, pp 299–308

Characterization of Phospholipid Mixed Micelles by Translational Diffusion

  • James J. Chou
  • James L. Baber
  • Ad Bax
Article

DOI: 10.1023/B:JNMR.0000032560.43738.6a

Cite this article as:
Chou, J.J., Baber, J.L. & Bax, A. J Biomol NMR (2004) 29: 299. doi:10.1023/B:JNMR.0000032560.43738.6a

Abstract

The concentration dependence of the translational self diffusion rate, Ds, has been measured for a range of micelle and mixed micelle systems. Use of bipolar gradient pulse pairs in the longitudinal eddy current delay experiment minimizes NOE attenuation and is found critical for optimizing sensitivity of the translational diffusion measurement of macromolecules and aggregates. For low volume fractions Φ (Φ ≤ 15% v/v) of the micelles, experimental measurement of the concentration dependence, combined with use of the Ds=Do(1-3.2λΦ) relationship, yields the hydrodynamic volume. For proteins, the hydrodynamic volume, derived from Ds at infinitely dilute concentration, is found to be about 2.6 times the unhydrated molecular volume. Using the data collected for hen egg white lysozyme as a reference, diffusion data for dihexanoyl phosphatidylcholine (DHPC) micelles indicate approximately 27 molecules per micelle, and a critical micelle concentration of 14 mM. Differences in translational diffusion rates for detergent and long chain phospholipids in mixed micelles are attributed to rapid exchange between free and micelle-bound detergent. This difference permits determination of the free detergent concentration, which, for a high detergent to long chain phospholipid molar ratio, is found to depend strongly on this ratio. The hydrodynamic volume of DHPC/POPC bicelles, loaded with an M2 channel peptide homolog, derived from translational diffusion, predicts a rotational correlation time that slightly exceeds the value obtained from peptide 15N relaxation data.

bicelledetergentDHPClysolipidhydrationNMRrelaxationself diffusion

Copyright information

© Kluwer Academic Publishers 2004

Authors and Affiliations

  • James J. Chou
    • 1
  • James L. Baber
    • 2
  • Ad Bax
    • 2
  1. 1.Department of Biological Chemistry & Molecular PharmacologyHarvard Medical SchoolBostonU.S.A
  2. 2.Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney DiseasesNational Institutes of HealthBethesdaU.S.A