Fig. 4: Cu⁺ entry.

a Electrostatic surface representation of the determined CopA structure. CopZ docking was performed with pyDockWEB⁴⁵ using a homology model of the C-terminal part of AfCopZ (see Methods for details). b Ensemble refinement around the Cu⁺ entry site yielded multiple possible orientations of the M158 side chain. The electrostatic surface is shown for three selected ensembles (I-III), illustrating that modest reorientations have a major impact. c Model for Cu⁺ uptake based on CopZ docking and ensemble refinement. A transient Cu⁺ uptake site is likely formed by the Cu⁺-coordinating residues (the so-called CxxC motif) of CopZ and M158, adopting an upward-facing side chain conformation similar to ensemble II. Cu⁺ transfer from CopZ directly to M158 is possible, likely without involvement of E205 and D336 that were previously proposed to be involved in ion uptake^16,24. Reorientation of M158 leads to formation of the transient Cu⁺ entry site detected in our data together with C380 and C382 of the CPC motif in M4. d Anomalous data collected at the Cu edge compatible with the presence of a Cu⁺ ion bound to C382 at the entry site. The final 2Fo-Fc and anomalous difference maps are shown in blue and brown mesh, respectively.