TROSY relaxation-optimized

The cross-correlation effects between the DD and CSA interactions also influence the transverse relaxation and lead to the phenomenon known as differential line broadening in a doublet [40], cf Figure Bl.13.8. There is a recent experiment, designed for protein studies, that I wish to mention at tire end of this section. It has been proposed by Pervushin etal [4T], is called TROSY (transverse relaxation optimized spectroscopy) and... 

For completeness, transverse relaxation-optimization is not limited to the constructive interference between DD coupling and CSA. Pervushin et al. [12] introduced the ZQ-TROSY, which is based on cross-correlated relaxation between H CSA and 15N CSA during the multiple quantum 15N-evolution period. 

SQ TOCSY TROSY ZQ ZQC single quantum total correlation spectroscopy transverse relaxation-optimized spectroscopy zero quantum zero-quantum coherence... 

New techniques for data analysis and improvements in instrumentation have now made it possible to carry out stmctural and conformational studies of biopolymers including proteins, polysaccharides, and nucleic acids. NMR, which may be done on noncrystalline materials in solution, provides a technique complementary to X-ray diffraction, which requires crystals for analysis. One-dimensional NMR, as described to this point, can offer structural data for smaller molecules. But proteins and other biopolymers with large numbers of protons will yield a very crowded spectrum with many overlapping lines. In multidimensional NMR (2-D, 3-D, 4-D), peaks are spread out through two or more axes to improve resolution. The techniques of correlation spectroscopy (COSY), nuclear Overhausser effect spectroscopy (NOESY), and transverse relaxation-optimized spectroscopy (TROSY) depend on the observation that nonequivalent protons interact with each other. By using multiple-pulse techniques, it is possible to perturb one nucleus and observe the effect on the spin states of other nuclei. The availability of powerful computers and Fourier transform (FT) calculations makes it possible to elucidate structures of proteins up to 40,000 daltons in molecular mass and there is future promise for studies on proteins over 100,000... 

TNO—Netherlands Organisation for Applied Scientific Research TROSY—transverse relaxation-optimized spectroscopy... 

Thus we cannot escape the depressing reality that 7 2 will get shorter and linewidth will get bigger as we increase the size of the protein studied. The reduced T2 is not only a problem for linewidth, but also causes loss of sensitivity as coherence decays during the defocusing and refocusing delays (1/(2J)) required for INEPT transfer in our 2D experiments. The only ray of hope comes in the form of a new technique called TROSY (transverse relaxation optimized spectroscopy), which takes advantage of the cancellation of dipole-dipole relaxation by CSA relaxation to get an effectively much longer 7 2 value we will briefly discuss TROSY at the end of this chapter. 

NEW TECHNIQUES FOR PROTEIN NMR RESIDUAL DIPOLAR COUPLINGS AND TRANSVERSE RELAXATION OPTIMIZED SPECTROSCOPY (TROSY)... 

A number of recently developed methods offer the potential for improving the quality of NMR structures and for increasing the size of proteins that will be examined. In particular, the use of residual dipolar couplings and of anisotropic contributions to relaxation provide new kinds of restraints that promise to lead to more accurate NMR structures.78 80 The recently developed TROSY (transverse relaxation optimized spectroscopy) method81 exploits relaxation phenomena to produce spectra with narrow lines, and promises to significantly expand the size of protein targets that can be examined by NMR from the current limit of 35 kDa to perhaps 150 kDa. 

Other problems arise if the complex that is formed is of high molecular weight - in this case the T2 relaxation time, which depends on the molecular weight, causes broadening of the resonances, although this problem can be overcome by the use of relaxation-optimized (TROSY) techniques. 

The exploitation of cross-correlation effects in high magnetic fields has introduced a new form of NMR spectroscopy called transverse relaxation-optimised spectroscopy or TROSY. The cross-correlation of the optimised dipole-dipole (DD) and chemical shift anisotropy (CSA) relaxation mechanisms leads to differential transverse relaxation rates for the two components of the l5N- H doublet in undecoupled spectra of l5N-labelled proteins. For one component, DD and CSA relaxation constructively add to produce very efficient relaxation, leading to a broad line, whereas for the other component, the two relaxation mechanisms constructively interfere, leading to a narrow line when the two mechanisms are nearly equal. There is no optimum field where DD and CSA relaxation are equal for all amide bonds, because DD relaxation between the amide protons and other nearby protons differs for each residue.72 Clearly, the overall effectiveness of TROSY is optimized when the non-exchangeable protons in the macromolecule... 

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