Extended Data Figure 5. A Zn²⁺ binding site was identified by X-ray fluorescence emission (Xfe) analysis of the CCR2-T4L:BMS-681:CCR2-RA-[R] crystals.

a, View of the Zn²⁺ ion at an interface formed by CCR2 helices III and VI and the N-terminus of T4L. The Zn²⁺ ion is coordinated by side chains of H144^3.56 (from WT receptor), E238^6.30 (from the engineered part of the receptor), and E1005 (from T4L) as well as a structured water. b, The background fluorescence signal of an empty MiTeGen micromount is low, indicating the absence of metal ion. Excitation at 12 keV results in a peak at 11.7 keV (due to the incidence beam). c, Xfe signal from a wide fluorescence scan of the CCR2-T4L crystal. The fluorescence peaks at 8.60 keV and 9.53 keV correspond to X-ray emission lines K_α (8.64 keV) and K_β (9.57 keV) and indicate the presence of Zn²⁺ bound to CCR2-T4L. d, A zoomed-in view of the Xfe signal from (c).