FIGURE 3.

Determination of the CXCR4 interface on SDF-1α by the methyl-TCS experiments. A, ratio of signal intensity reductions originating from the isoleucine, leucine, and valine methyl resonances, with and without irradiation. The purple bars represent the ratios from the methyl-TCS experiment (Fig. 2, A and C), and the green bars represent those from the negative control experiment (Fig. 2, B and D). The ratios for the Val^18γ1 and Val^49γ2 signals were not determined (N.D.), because these two signals were severely overlapped. The error bars represent the experimental errors, calculated from the root sum square of (noise level/signal intensity) in the two spectra, with and without irradiation. B, differences in the signal reduction ratios (ΔRR values) between the methyl-TCS experiment (purple bars in A) and the control experiment (green bars in A). The error bars represent the experimental errors, calculated from the root sum square of errors in two experiments. Red, light red, orange, and cyan bars represent the signals with ΔRR > 0.150, 0.125, 0.100, and <0.100, respectively. Methyl protons completely buried in the structures are shaded in gray. C, mapping of the affected residues on the SDF-1α structure (Protein Data Bank code 1VMC). The SDF-1α structure is shown in a CPK representation. Isoleucine, leucine, and valine residues are colored according to the ΔRR values of their methyl resonances, as in B. For the leucine and valine residues, the larger ΔRR of their two methyl resonances was utilized.