Autori: C. Jaroniec, C. Filip, R.G. Griffin

Editorial: J. Am. Chem. Soc., 124, p.10729-1074, 2002.

Rezumat:

We describe three-dimensional magic-angle-spinning NMR experiments for the simultaneous
measurement of multiple carbon-nitrogen distances in uniformly 13C,15N-labeled solids. The approaches
employ transferred echo double resonance (TEDOR) for 13C-15N coherence transfer and 15N and 13C
frequency labeling for site-specific resolution, and build on several previous 3D TEDOR techniques. The
novel feature of the 3D TEDOR pulse sequences presented here is that they are specifically designed to
circumvent the detrimental effects of homonuclear 13C-13C J-couplings on the measurement of weak 13C-
15N dipolar couplings. In particular, homonuclear J-couplings lead to two undesirable effects: (i) they generate
anti-phase and multiple-quantum (MQ) spin coherences, which lead to spurious cross-peaks and phasetwisted
lines in the 2D 15N-13C correlation spectra, and thus degrade the spectral resolution and prohibit
the extraction of reliable cross-peak intensities, and (ii) they significantly reduce cross-peak intensities for
strongly J-coupled 13C sites (e.g., CO and CR). The first experiment employs z-filter periods to suppress
the anti-phase and MQ coherences and generates 2D spectra with purely absorptive peaks for all TEDOR
mixing times. The second approach uses band-selective 13C pulses to refocus J-couplings between 13C
spins within the selective pulse bandwidth and 13C spins outside the bandwidth. The internuclear distances
are extracted by using a simple analytical model, which accounts explicitly for multiple spin-spin couplings
contributing to cross-peak buildup. The experiments are demonstrated in two U-13C,15N-labeled peptides,
N-acetyl-L-Val-L-Leu (N-ac-VL) and N-formyl-L-Met-L-Leu-L-Phe (N-f-MLF), where 20 and 26 13C-15N
distances up to 5-6 Å were measured, respectively. Of the measured distances, 10 in N-ac-VL and 13
in N-f-MLF are greater than 3 Å and provide valuable structural constraints. We describe three-dimensional magic- angle-spinning NMR experiments for the simultaneous measurement of multiple carbon-nitrogen distances in uniformly 13C,15N-labeled solids. The approaches
employ transferred echo double resonance (TEDOR) for 13C-15N coherence transfer and 15N and 13C frequency labeling for site-specific resolution, and build on several previous 3D TEDOR techniques. The novel feature of the 3D TEDOR pulse sequences presented here is that they are specifically designed to
circumvent the detrimental effects of homonuclear 13C-13C J-couplings on the measurement of weak 13C-15N dipolar couplings. In particular, homonuclear J-couplings lead to two undesirable effects: (i) they generate anti-phase and multiple-quantum (MQ) spin coherences, which lead to spurious cross-peaks and phasetwisted lines in the 2D 15N-13C correlation spectra, and thus degrade the spectral resolution and prohibit the extraction of reliable cross-peak intensities, and (ii) they significantly reduce cross-peak intensities for strongly J-coupled 13C sites (e.g., CO and CR). The first experiment employs z-filter periods to suppress the anti-phase and MQ coherences and generates 2D spectra with purely absorptive peaks for all TEDOR mixing times. The second approach uses band-selective 13C pulses to refocus J-couplings between 13C spins within the selective pulse bandwidth and 13C spins outside the bandwidth. The internuclear distances are extracted by using a simple analytical model, which accounts explicitly for multiple spin-spin couplings contributing to cross-peak buildup. The experiments are demonstrated in two U-13C,15N-labeled peptides, N-acetyl-L-Val-L-Leu (N-ac-VL) and N-formyl-L-Met-L-Leu-L-Phe (N-f-MLF), where 20 and 26 13C-15N distances up to 5-6 Å were measured, respectively. Of the measured distances, 10 in N-ac-VL and 13 in N-f-MLF are greater than 3 Å and provide valuable structural constraints.

Cuvinte cheie: RMaleNe structur in soldide, proteine, investigar // solid state nmr, proteins, structure determintion