Solid-state NMR in biomembranes

Chapter 8 complements the previous chapter and develops the basic theory needed to understand how solid-state NMR can be utilized in membrane systems. In particular it shows that wide line NMR can be sensitive to molecular motions and that it is an appropriate tool to track membrane dynamics (membrane fiuidity, fusion) and probe average orientations of molecules embedded in membranes (membrane topology). The three-dimensional structure of molecules in membranes can also be obtained by making use of magic angle sample spinning, a technique that leads to 

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In the 1970s the structure and dynamics of lipid bilayer membranes were extensively investigated by NMR. The principles of the NMR spectroscopy applied to the study of biomembranes are reviewed in Ref. 5, together with the fruitful achievements in the early stage. In the 1980s the NMR biomembrane research was carried out mainly by applying the solid-state NMR techniques [6-11]. Generally, the solid-state spectra are of low reso-... 

Abstract To understand how membrane-active peptides (MAPs) function in vivo, it is essential to obtain structural information about them in their membrane-bound state. Most biophysical approaches rely on the use of bilayers prepared from synthetic phospholipids, i.e. artificial model membranes. A particularly successful structural method is solid-state NMR, which makes use of macroscopically oriented lipid bilayers to study selectively isotope-labelled peptides. Native biomembranes, however, have a far more complex lipid composition and a significant non-lipidic content (protein and carbohydrate). Model membranes, therefore, are not really adequate to address questions concerning for example the selectivity of these membranolytic peptides against prokaryotic vs eukaryotic cells, their varying activities against different bacterial strains, or other related biological issues. 

Esteban-Martin S, Strandberg E, Salgado J, Ulrich AS (2010) Solid state NMR analysis of peptides in membranes influence of dynamics and labeling scheme. BBA-biomembranes 1798 252-257... 

An inspection of Table 9.1 reveals that has similar NMR properties to H. Thus, methods which deal with the residual broadening due to homonudear dipolar couplings are also of much relevance in solid-state NMR [57]. Although fluorine is much less commonly encountered in chemistry than the omnipresent hydrogen, F solid-state NMR has found a number of important applications, with recent examples including fluoropolymers [58] and biomembranes [59]. 

Solid-state NMR studies of biomembranes have been carried out with deuterium or phosphorus-31. H-NMR spectroscopy has been of great help in the study of the physical state of the hydrocarbon chain region of phospholipid bilayers (Smith, 1979 Chan et al, 1981). This requires the synthesis of specifically deut-erated phospholipids. These lipids are then dispersed... 

Globular and membrane proteins in aqueous solution or Hpid bilayers/ biomembranes could undergo a wide range of motions at ambient temperatures. Such motions can be characterized by several types of NMR relaxation parameters, chemical exchange, dynamic interference including SRI [27—29]. Detection ranges for motions by the respective parameters are schematically illustrated in Fig. 1.1 for solution and soUd state NMR approaches. Naturally, fast motions are solely examined by solution NMR techniques for any portions of proteins. The experimental approaches to be able to detect intermediate or slow motions are obviously different between the solution and solid state NMR methods. 

Solid-state F solid-state NMR spectroscopy are used to analyze the structure and dynamics of lipophilic drugs and peptides embedded in biomembranes. Here experiments using the homonuclear dipolar couplings of trifluoromethyl labels can provide valuable parameters such as orientational constraints and/or distances. 

Here, we discuss a solid-state 19F-NMR approach that has been developed for structural studies of MAPs in lipid bilayers, and how this can be translated to measurements in native biomembranes. We review the essentials of the methodology and discuss key objectives in the practice of 19F-labelling of peptides. Furthermore, the preparation of macroscopically oriented biomembranes on solid supports is discussed in the context of other membrane models. Two native biomembrane systems are presented as examples human erythrocyte ghosts as representatives of eukaryotic cell membranes, and protoplasts from Micrococcus luteus as membranes... 

Tremouilhac P, Strandberg E, Wadhwani P, Ulrich AS (2006) Conditions affecting the realignment of the antimicrobial peptide PGLa in membranes as monitored by solid state H-2-NMR. BBA-Biomembranes 1758 1330-1342... 

Ulrich, A. S. (2005) Solid state F-19 NMR methods for studying biomembranes. Progress in Nuclear Magnetic Resonance Spectroscopy, 46(1), 1-21. 

Solid-state F NMR of biological samples has been reviewed by Ulrich. The methodological aspects were the focus of this review article, with an emphasis on designated techniques for studying biomembranes. The unique properties of the F nucleus, the most informative NMR parameters, the special hardware requirements, and appropriate pulse sequences were considered. Following these experimental aspects, several applications of F NMR have been highlighted, for example, for the characterisation of the F CSA tensors of relevant amino acids and for the examination of the behaviour of drugs in lipid bilayers. 

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