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The fact that membrane proteins are notoriously difficult to analyse using standard protocols for atomic-resolution structure determination methods have motivated adaptation of these techniques to membrane protein studies as well as development of new technologies. With this motivation, liquid-state nuclear magnetic resonance (NMR) has recently been used with success for studies of peptides and membrane proteins in detergent micelles, and solid-state NMR has undergone a tremendous evolution towards characterization of membrane proteins in native membrane and oriented phospholipid bilayers. In this mini-review, we describe some of the technological challenges behind these efforts and provide examples on their use in membrane biology. [ABSTRACT FROM AUTHOR]

The quadrupole Carr-Purcell-Meiboom-Gill NMR experiment using magic-angle spinning (QCPMG-MAS) is analysed as a means of determining quadrupolar coupling and anisotropic chemical shielding tensors for half-integer I > 1/2 quadrupolar nuclei with large quadrupole coupling constants C . This is accomplished by numerical simulations and 87Rb NMR experiments wih Rb SO and Rb CrO using different magnetic fields. It is demonstrated that (i) QCPMG-MAS experiments typically provide a sensitivity gain by more than an order of magnitude relative to quadrupolar-echo MAS experiments, (ii) non-secular secondorder terms do not affect the spin evolution appreciably, and (iii) the effect of finite RF pulses needs to be considered when 2omega2Q/omega0omega RF > 0.1, where omegaQ = 2piC Q/4I2I1I - 1, omegaRF is the RF amplitude, and omega0 the Larmor frequency. Using numerical simulations and iterative fitting the magnitudes and relative orientation of 87Rb quadrupolar coupling and chemical shielding tensors for Rb2SO4 and Rb2CrO4 have been determined. [ABSTRACT FROM AUTHOR]