Fig 3.

Measurement of carbon–nitrogen internuclear distances in [U-¹³C,¹⁵N]f-MLF-OH by frequency-selective REDOR (16). (a) Structural model of f-MLF-OH displaying the distances measured in b–d. Experimental REDOR S/S₀ curves (S₀ and S represent the reference and dipolar dephasing experiments, respectively) and simulations are shown for Met(C^β)–Leu(N) (b), Leu(C^δ)–Leu(N) (c), and Met(C^β)–Phe(N) (d), and they correspond to internuclear distances of 3.12 ± 0.03 Å (b), 3.64 ± 0.09 Å (c), and 4.12 ± 0.15 Å (d). A total of 16 distances between 2.5 and 6 Å were measured in f-MLF-OH. Distance measurements were performed in a sample prepared by cocrystallizing [U-¹³C,¹⁵N]f-MLF-OH with natural-abundance f-MLF-OH in a 1:9 ratio, to minimize the interference from intermolecular ¹³C–¹⁵N couplings. Details of the pulse sequence and experimental parameters can be found in ref. 16.