FIGURE 2.

2D ¹H–¹³C MELODI–HETCOR and ¹H–¹⁵N HETCOR spectra of the oat phyA3 u-[¹³C,¹⁵N]-PCB chromophore as Pfr. (A) The MELODI–HETCOR spectrum acquired with an LG–CP contact time of 500 μs (red) reveals mostly intramolecular ¹H contacts of the chromophore carbons (for example, ¹H^{N21 - N24}–¹³C^PCB, marked × in black). Heteronuclear signals obtained with a mixing period of 900 μs (purple) fall into two categories: (i) Intramolecular ¹H^{N21 - N24}–¹³C^PCB correlations (marked × in black and green for fully and less resolved signals, respectively), and (ii) interfacial correlations between the chromophore and protein residues in its vicinity (shaded in gray). Intramolecular ¹H^{N21 - N24}–¹³C^PCB correlations are summarized in Supplementary Table S2. (B) The ¹H–¹⁵N HETCOR spectrum was acquired for tracing direct ¹H–¹⁵N connectivities. For all three correlation spectra, only the characteristic spectral region of δ^H = 8–13 ppm (ω₁-dimension) is shown. δ^H and δ^C/(δ^N) values are indicated by the horizontal and vertical lines, respectively. The 1D ¹³C and ¹⁵N MAS spectra of the same protein as Pfr are shown with assignments as the external projections along the ω₂-dimension above the spectra in (A,B), respectively. Resonances marked with an asterisk indicate glycerol carbons and amide nitrogens of protein backbone originating from ¹³C and ¹⁵N in natural abundance.