1 However, a great deal of progress in obtaining high-resolution structures of membrane proteins using crystallography and solution NMR methods has recently been made.

While structural studies using solution NMR and crystallography have provided significant insights into the functional aspects of water-soluble molecules, extension of such studies to membrane-associated molecules has been a challenge. As a first application, these solid-state NMR approaches were utilized to probe the membrane interaction of an antidepressant molecule, desipramine, and its location in the membrane.

In these 2D experiments, natural abundance 13C was observed from bicelles containing DMPC and DHPC lipid molecules.

An extension of this approach to accurately measure 13C- 31P and 1H- 31P couplings from phospholipids, which are useful to understand the interaction of molecules with the membrane, is also described. Furthermore, we demonstrate that a laboratory-frame separated-local-field experiment is capable of overcoming these difficulties in magnetically aligned bicelles. In the present study, we demonstrate that the PISEMA and other rotating-frame pulse sequences are not suitable for the measurement of long-range heteronuclear dipolar couplings, and that they provide inaccurate values when multiple protons are coupled to a 13C nucleus.

These studies commonly utilize the PISEMA pulse sequence to measure dipolar coupling and chemical shift, the two key parameters used in subsequent structural analysis. Magnetically aligned bicelles are increasingly being used as model membranes in solutionand solid-state NMR studies of the structure, dynamics, topology, and interaction of membraneassociated peptides and proteins.

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