Figure 7.

¹³C-detected ¹H T₂ relaxation data of M2TM-AH in oriented bicelles at 302 K under the static condition. (a) Pulse sequence of the dipolar-dephased ¹H T₂ relaxation experiment used to obtain the data in (g). (b) Representative ¹³C spectra without dipolar dephasing, measured with 10 ms ¹H spin diffusion. (c) Representative ¹³C spectra without dipolar dephasing, measured with 100 ms ¹H spin diffusion. (d) Representative ¹³C spectra with dipolar dephasing and 100 ms ¹H spin diffusion. The echo delay is 0 for all the spectra in (b–d). (e) ¹³C-detected ¹H T₂ relaxation curves with 10 ms spin diffusion. The schematic illustration below indicates that ¹H magnetization transfer is mostly within the peptide at this mixing time. (f) ¹³C-detected ¹H T₂ relaxation curves after 100 ms spin diffusion. At this mixing time, lipid ¹H magnetization from the surrounding environment is transferred to the peptide, thus giving much slower relaxation. A fast initial decay is especially pronounced for the L26 Cb signal. (g) ¹H T₂ relaxation curves measured with 100 μs C-H dipolar dephasing and 100 ms spin diffusion, to selectively detect the T₂ relaxation of lipids near the peptide. The disappearance of the fast initial decay of the L26 Cb data verifies that the origin of the fast initial decay is the rigid peptide protons.