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Triple-resonance nuclear magnetic resonance spectroscopy
Triple resonance experiments are a set of multi-dimensional nuclear magnetic resonance spectroscopy (NMR) experiments that link three types of atomic nuclei, most typically consisting of 1H, 15N and 13C. These experiments are often used to assign specific resonance signals to specific atoms in an isotopically enriched protein. The technique was first described in papers by Ad Bax, Mitsuhiko Ikura and Lewis Kay in 1990, and further experiments were then added to the suite of experiments. Many of these experiments have since become the standard set of experiments used for the sequencing assignment of resonances of protein necessary for the determination of protein structure by NMR, and are an integral part of solution NMR study of proteins.〔
==Background==
There are two main methods of determining protein structure on the atomic level. The first of these is by X-ray crystallography, starting in 1958 when the crystal structure of myoglobin was determined. The second method is by NMR, which began in the 1980s when Kurt Wüthrich outlined the framework for NMR structure determination of proteins, and solved the solution structure of small globular proteins. Structural determination of protein by NMR however requires the assignment of the NMR signals from the many nuclei in the protein. The early method of protein NMR relied on proton-based homonuclear NMR spectroscopy where the size of the protein that may be determined is limited to ~10 KDa. This limitation is due to the presence of greater number of protons in larger protein which results in overcrowding of the resonances, as well as the broadening of signal that comes with increasing size of protein, making resonance assignment difficult. These problems may be alleviated by using heteronuclear NMR spectroscopy which allows the proton spectrum to be edited with respect to the 15N and 13C chemical shifts, as well as increasing the number of dimension of the spectrum. In 1990, Ad Bax and coworkers developed the triple resonance technology and experiments on proteins isotopically-labelled with 15N and 13C,〔 with the result that the spectra are dramatically simplified, greatly facilitating the process of resonance assignment, and increasing the size of the protein that may be determined by NMR.
These triple resonance experiments utilize the relatively large magnetic couplings between certain pairs of nuclei to establish their connectivity. Specifically, the 1JNH, 1JCH, 1JCC, and 1JCN couplings are used to establish the scalar connectivity pathway between nuclei. The magnetization transfer process takes place through multiple, efficient one-bond magnetization transfer steps, rather than a single step through the smaller and variable 3JHH couplings. The relatively large size and good uniformity of the one-bond couplings allowed the design of efficient magnetization transfer schemes that are effectively uniform across a given protein, nearly independent of conformation. Triple resonance experiments involving 31P may also be use for nucleic acid studies.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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