Review Article Solid-state NMR Structure Determination Alison Drechsler and Frances Separovic School of Chemistry, University of Melbourne, Melbourne, VIC 3010, Australia Summary Biological applications of solid-state NMR (SS-NMR) have been predominantly in the area of model membrane systems. Increasingly the focus has been membrane peptides and proteins. SS-NMR is able to provide information about how the peptides or proteins interact with the lipids or other peptides/proteins in the membrane, their effect on the membrane and the location of the peptides or proteins relative to the membrane surface. Recent developments in biological SS-NMR have been made possible by improvements in labelling and NMR techniques. This review discusses aligned systems and magic angle spinning techniques, bilayers and bicelles, and measurement of chemical shift anisotropy and dipolar coupling. A number of specific experiments such as cross polarization, rotational resonance, REDOR, PISEMA, MAOSS and multidimensional experiments are described. In addition to 2 H, 13 C and 15 N, recent solid-sate 1 H, 19 F and 17 O NMR work is discussed. Several examples of the use of SS-NMR to determine the structure of membrane peptides and proteins are given. IUBMB Life, 55: 515–523, 2003 Keywords Solid-state NMR; protein structure; membrane peptides. INTRODUCTION NMR spectroscopy has been embraced by structural biology, primarily to determine the structure of proteins in the solution-state. Increasingly, solid-state NMR spectroscopy is being used to determine the structure of biologically important molecules. In comparison to solution NMR, solid-state NMR (SS-NMR) has been less regularly applied to biological samples due to limitations caused by extreme line broadening and poor sensitivity (1). However, in recent years new techniques have been developed that allow these limitations to be reduced, manipulated and even exploited to provide the NMR spectroscopist with a large amount of structural information that is difficult to obtain by other techniques. One area in which biological SS-NMR has found increasing application is the investigation of membrane proteins, in particular, determination of interactions with lipid membranes and any structural or conformational changes that occur (2). Membrane proteins are not readily soluble in aqueous solution, are often difficult to crystallize and, especially when embedded in a membrane system, have a large molecular weight. Hence membrane proteins are not usually amenable to the two main techniques of structural biology, X-ray diffraction and solution NMR spectroscopy. SS-NMR techniques, however, are applicable to biological systems such as membrane proteins and complexes that are relatively immobile, or undergoing slow motions in compar- ison to NMR timescales. SS-NMR has been applied to model membranes for decades (3) and with recent improve- ments in spectral quality, is increasingly being applied to structural studies of membrane peptides, transmembrane segments of proteins and membrane proteins themselves. We have been using SS-NMR to determine the interaction of a pore-forming protein with phospholipid membranes (4) and are extending this work using labelled protein to determine structural changes following membrane insertion. SS-NMR is able to provide information about the interaction of proteins or peptides with lipid bilayers, which are more representative of a biological membrane than a hydrophobic solvent or detergent micelles. The peptide conformation or orientation relative to the membrane surface can be obtained under static conditions using aligned phospholipid multilayers (5, 6), or magic angle spinning (MAS) techniques can be used to enhance spectral resolution to gain structural information Received 3 July 2003; accepted 26 August 2003 Address correspondence to Frances Separovic. Fax + 61 3 9347 5180. E-mail: fs@unimelb.edu.au Abbreviations: BPTI, Basic Pancreatic Trypsin Inhibitor; CP, Cross Polarization; CSA, Chemical Shift Anisotropy; CRAMPS, Combined Rotation and Multiple-Pulse Spectroscopy; FSR, Fre- quency Selective REDOR; HIV, Human Immunodeficiency Virus; MAS, Magic Angle Spinning; MAOSS, Magic Angle Oriented Sample Spinning; MQ, Multiple Quantum; MAT, Magic Angle Turning; NMR, Nuclear Magnetic Resonance; REDOR, Rotational- Echo Double-Resonance; PISEMA, Polarization Spin Exchange at the Magic Angle; PDSD, Proton-Driven Spin Diffusion; PISA; Polarity Index Slant Angle; R 2 , Rotational Resonance; RF, Radio Frequency; SS-NMR, Solid-state NMR; TOSS, Total Suppression of Sidebands. IUBMB Life, 55(9): 515–523, September 2003 ISSN 1521-6543 print/ISSN 1521-6551 online # 2003 IUBMB DOI: 10.1080/15216540310001622740