Figure 4.

2D and 3D MAS NMR. (a) 2D ¹³C-¹³C spectrum on 1.7 mg oxidized ¹³C,¹⁵N-cyt-c bound to DOPC/TOCL LUVs, obtained with 10 ms DARR mixing. Selected residue types are indicated and the dashed box marks Ala C^α-C^β crosspeaks. The spectrum was processed with fourfold zero-filling after 15 Hz Lorentzian line sharpening and 40 or 50 Hz Gaussian line broadening in the direct and indirect dimensions, respectively. (b) Enlargement of the Ala C^β-C^α crosspeaks; (c) Analogous (simulated) peaks from solution NMR data (46) on the soluble protein (see text for details). (d) 2D slices from a 3D NCACX spectrum reveal distinct Ala signals (black X), at ¹⁵N shifts shown at bottom right. Tentative assignments based on correspondence to solution NMR shifts are indicated. (e) MAS NMR secondary chemical shifts Δδ(C^α-C^β) deviate from random coil values (at zero) and indicate mostly α-helical structure for the Ala, in line with the native structure (Fig. 1a). Dashed lines at ±0.7 ppm indicate the typical boundaries to the random coil regime. Experiments performed at 233 K, 8.33 kHz MAS, and 600 MHz (for ¹H). To see this figure in color, go online.