Frequency selective heteronuclear dipolar recoupling in rotating solids: accurate (13)C-(15)N distance measurements in uniformly (13)C,(15)N-labeled peptides.
We describe a magic-angle spinning NMR experiment for selective (13)C-(15)N distance measurements in uniformly (13)C,(15)N-labeled solids, where multiple (13)C-(15)N and (13)C-(13)C interactions complicate the accurate measurement of structurally interesting, weak (13)C-(15)N dipolar couplings. The new experiment, termed FSR (frequency selective REDOR), combines the REDOR pulse sequence with a frequency selective spin-echo to recouple a single (13)C-(15)N dipolar interaction in a multiple spin system. Concurrently the remaining (13)C-(15)N dipolar couplings and all (13)C-(13)C scalar couplings to the selected (13)C are suppressed. The (13)C-(15)N coupling of interest is extracted by a least-squares fit of the experimentally observed modulation of the (13)C spin-echo intensity to the analytical expression describing the dipolar dephasing in an isolated heteronuclear spin pair under conventional REDOR. The experiment is demonstrated in three uniformly (13)C,(15)N-labeled model systems: asparagine, N-acetyl-L-Val-L-Leu and N-formyl-L-Met-L-Leu-L-Phe; in N-formyl-[U-(13)C,(15)N]L-Met-L-Leu-L-Phe we have determined a total of 16 internuclear distances in the 2.5-6 A range.
Jaroniec
C P
CP
Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Tounge
B A
BA
Herzfeld
J
J
Griffin
R G
RG
D001216:Asparagine / Q000737:chemistry*; D002250:Carbon Radioisotopes; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008968:Molecular Conformation; D009590:Nitrogen Radioisotopes; D010455:Peptides / Q000737:chemistry*
D002250:Carbon Radioisotopes; D009590:Nitrogen Radioisotopes; D010455:Peptides; D001216:Asparagine