Frequency Selective Heteronuclear Dipolar Recoupling in Rotating Solids:  Accurate 13C−15N Distance Measurements in Uniformly 13C,15N-labeled Peptides

• Published in: Journal of the American Chemical Society 2001-04, Vol.123 (15), p.3507-3519
• Main Authors: Jaroniec, Christopher P, Tounge, Brett A, Herzfeld, Judith, Griffin, Robert G
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja003266e

We describe a magic-angle spinning NMR experiment for selective 13C−15N distance measurements in uniformly 13C,15N-labeled solids, where multiple 13C−15N and 13C−13C interactions complicate the accurate measurement of structurally interesting, weak 13C−15N 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 13C−15N dipolar interaction in a multiple spin system. Concurrently the remaining 13C−15N dipolar couplings and all 13C−13C scalar couplings to the selected 13C are suppressed. The 13C−15N coupling of interest is extracted by a least-squares fit of the experimentally observed modulation of the 13C 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 13C,15N-labeled model systems:  asparagine, N-acetyl-l-Val-l-Leu and N-formyl-l-Met-l-Leu-l-Phe; in N-formyl-[U-13C,15N]l-Met-l-Leu-l-Phe we have determined a total of 16 internuclear distances in the 2.5−6 Å range.