Frequency selective heteronuclear dipolar recoupling in rotating solids: Accurate C-13-N-15 distance measurements in uniformly C-13,N-15-labeled peptides
Cp. Jaroniec et al., Frequency selective heteronuclear dipolar recoupling in rotating solids: Accurate C-13-N-15 distance measurements in uniformly C-13,N-15-labeled peptides, J AM CHEM S, 123(15), 2001, pp. 3507-3519
We describe a magic-angle spinning NMR experiment for selective C-13-N-15 d
istance measurements in uniformly C-13,N-15-labeled solids, where multiple
C-13-N-15 and C-13-C-13 interactions complicate the accurate measurement of
structurally interesting, weak C-13-N-15 dipolar couplings. The new experi
ment, termed FSR (frequency selective REDOR), combines the REDOR pulse sequ
ence with a frequency selective spin-echo to recouple a single C-13-N-15 di
polar interaction in a multiple spin system. Concurrently the remaining C-1
3-N-15 dipolar couplings and all C-13-C-13 scalar couplings to the selected
C-13 are suppressed. The C-13-N-15 coupling of interest is extracted by a
least-squares fit of the experimentally observed modulation of the C-13 spi
n-echo intensity to the analytical expression describing the dipolar dephas
ing in an isolated heteronuclear spin pair under conventional REDOR. The ex
periment is demonstrated in three uniformly C-13,N-15-labeled model systems
: asparagine, N-acetyl-L-Val-L-Leu acid N-formyl-L-Met-L-Leu-L-Phe; in N-fo
rmyl-[U-C-13,N-15]L-Met-L-Leu-L-Phe we have determined a total of 16 intern
uclear distances in the 2.5-6 Angstrom range.