AccA from Neisseria gonorrhoeae provides a new framework for understanding periplasmic copper metallochaperones

Many bacteria use copper (Cu) to drive key redox reactions and energy metabolism, and they often rely on metallochaperones to deliver Cu to Cu-dependent enzymes. However, why delivery by metallochaperones is needed, and why Cu cannot transfer directly from cellular pools to the target enzymes, is not well understood. Here, we show that the PCu_AC-family metallochaperone AccA from the periplasm of Neisseria gonorrhoeae delivers Cu to the Cu-dependent nitrite reductase AniA, enabling growth and nitrite respiration in O₂-limiting conditions. Although purified AccA binds both Cu(i) and Cu(ii) ions, only the Cu(i)-binding site is essential for activating AniA in N. gonorrhoeae cells. Unexpectedly, the Cu(i)-binding affinity of AniA is >50 times weaker than that of AccA, suggesting that Cu delivery occurs against a favourable affinity gradient. We propose that AccA is needed because AniA cannot compete with the periplasmic milieu for binding Cu, providing a new framework to understand why some Cu-dependent enzymes need metallochaperones to deliver Cu.