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Recent advances in structural biology have made possible the high-throughput structural determination of proteins, which is reflected in the very rapid growth of Protein Data Bank content. In structural proteomics, recombinant proteins used for structural determination by NMR spectroscopy and X-ray crystallography are conventionally produced by use of bacterial expression systems or recently by cell-free protein expression systems and therefore do not possess carbohydrate moieties. However, many of the proteins in the living systems are covalently linked to carbohydrate moieties, which mediate molecular recognition involved in cell-cell communication, contribute to solubility and structural integrity of proteins, and determine the fates of glycoproteins in cells, i.e. folding, transport, and degradation via interactions with a variety of intra-cellular lectins [1,2].

A human being has about one hundred thousand million cells. For the various types of cells to properly function, channels, valves, and gates are required. Channels are used to transport ions and small molecules, such as water, through cell membranes.

Integral membrane proteins, traversing the membrane once or several times as α-helices, play crucial roles in maintaining various activities of cells such as transport of appropriate molecules into or out of the cell, catalysis of chemical reaction, and receiving and transducing chemical signals from the cell environment. Naturally, biological activity of such proteins may depend upon their conformations and dynamics regulated by specific lipid-protein and/or protein-protein interactions as structural determinants, as studied by analysis of 2D assembly of bacteriorhodopsin (bR) as a typical membrane protein [1]. bR is active as a proton pump and considered as a proto-type of a variety of G-protein coupled receptors, consisting of seven transmembrane α-helices.

The inside of living cells is separated from the external environment and divided into functionally distinctive compartments by a variety of lipid membranes such as the plasma membrane, the endoplasmic reticulum membrane, the nuclear membrane, etc. Naturally, a number of important cellular functions depend on translocation of materials and transduction of signals between those compartments as results of regulated transports of proteins and small molecules between the membranes of the compartments. In fact, a number of proteins involved in the important cellular functions such as cellular signal transduction, regulation of the cytoskeleton, and regulation of the membrane structure have been known to interact with the membrane surfaces as parts of their functions. Although many of those proteins are classified as water-soluble proteins, important parts of their physiological functions are related to their transient membrane-binding states. In order to understand structure—function relationship of those membrane-binding proteins, the protein structures at the water-lipid bilayer interface should be investigated in detail and compared with those in the aqueous phase, since structural changes accompanying the translocation of the proteins from the aqueous phase to the membrane surface would alter the functions of the proteins at the membrane surfaces where they play important physiological roles.

In photosynthesis, light energy conversion proceeds in two steps [1]. First excitons are generated in antenna systems and subsequently charge separation takes place in reaction centers (RCs, Figure 1). To gain insight into the structural and functional properties of such active elements in photosynthesis, solid-state NMR is increasingly important. Here a number of examples of recent investigations are summarized, first structure-function studies of antennae and RCs, and second structure determination, including methodology development. To resolve molecular electron pumping mechanisms in bacterial RCs and to study the electronic structure of light-harvesting (LH) proteins, both global and specific assays of cofactors and protein side chains have been performed. Novel techniques allow a determination of structural models for self-assembled chlorophyll preparations in vitro and for the natural chlorosome antenna system. Finally, it is possible to perform sequence specific assignments of uniformly labeled complexes and to observe intermediate states in light-triggered reactions, produced by illumination of frozen samples in the spectrometer.

Since α-helices and turns (helix-turn-helix motif) are stabilized by short-range interactions, and since many membrane proteins are built around (transmembrane) helical bundles, much of the secondary structure of such membrane proteins can be captured in peptide fragments. Furthermore, if sufficient long-range point-to-point experimental distance constraints are available from the intact protein, a structure for the whole protein can be assembled from the structures of the peptide fragments. In this review, we will describe the basis for the first statement and give some examples of the second. The review will conclude with a brief look at the future of high-resolution NMR in the study of the structural biology of intact membrane proteins in detergent micelles.

One recent application of NMR concerns rheology [1,2], the study of the mechanical properties of fluids. This application has come to be known as “Rheo-NMR” [3–7].

Radiochemistry (tritium chemistry in particular) and nuclear magnetic resonance (NMR) spectroscopy are hardly ever taught within the same undergraduate degree course. This is one of the main reasons why those who become NMR spectroscopists are so reluctant to see radioactive material being used in their instruments. The main thrust for the development of ^3H NMR spectroscopy [1] has therefore come from the radiochemistry area and from those in the pharmaceutical and life sciences who appreciate the potential benefits of working with this radionuclide.

On-line coupling of Chromatographic systems to spectroscopic techniques, often called a “hyphenated technique” [1], has been proven to be an effective method for the analysis of complicated mixtures. Among such coupled systems, the hyphenation of liquid chromatography with NMR spectroscopy (LC-NMR) is a uniquely powerful and versatile combination, as NMR gives molecular-level structural information, with the advantage over other common LC detectors.

The nuclear Overhauser effect (NOE) is observed as a change in intensity of one resonance when the intensity of a neighboring resonance is perturbed. The effect depends strongly on the internuclear distance r , in that the rate of transmission of the NOE is proportional to r ^-6. However, various factors conspire to reduce this dependence, making reliable quantitation of distances difficult. Nevertheless, the technique is widely used, particularly in the structure determination of biomolecules and as a routine method for conformational analysis in chemistry. The introduction of new methodology has greatly extended its use for conformational analysis, measurement of intermolecular interactions, and analysis of ligand binding. Thus, although our understanding of the theory of the NOE has not changed much in recent years, the areas of application continue to increase.