The thylakoid lumen of the cyanobacterium Synechocystis PCC 6803 is supplied with copper via two copper-transporting ATPases and a metallochaperone intermediary. We show that the copper site of this metallochaperone is unusual and consists of two cysteine residues and a histidine imidazole located on structurally dynamic loops. Substitution of this histidine residue enhances bacterial two-hybrid interaction with the cytosolic copper exporter, but not the copper importer, suggesting that the interacting surfaces are distinct, with implications for metal transfer.

Abbreviations used: 2D, two-dimensional; 3D, three-dimensional; HSQC, heteronuclear single-quantum coherence; LB, Luria–Bertani; NOE, nuclear Overhauser effect.

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These authors made an equal contribution to this work.

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