A periplasmic metallochaperone of the Cation Diffusion Facilitator YiiP is required for Zn ²⁺ sensing in Pseudomonas aeruginosa

Pseudomonas aeruginosa thrive to survive in harsh conditions imposed by the host. We have previously described two Zn ²⁺ -transporting members of the Cation diffusion facilitator family, YiiP and CzcD, confering resistance to imipenem by decreasing the expression of the outer membrane porin OprD (A. Salusso and D. Raimunda, Frontiers in cellular and infection microbiology 7:84, 2017, https://doi.org/10.3389/fcimb.2017.00084 ). Here we provide evidence that a protein encoded in yiiP ’s operon, PA3962, is fundamental to the coupling of this process. Immunodetection assay indicates that PA3962 locates in membranes. Supporting a role in oprD regulation, an insertion mutant has increased imipenem sensitivity, which is suppressed by gene complementation but not in presence of Zn ²⁺ , as opposed to the YiiP mutant. We identified 2 pairs of conserved acidic residues in a hydrophobic juxtamembrane domain. Metal binding specificity and stoichiometry was explored in wild type and mutant versions of these. Zn ²⁺ is the cognate metal being D40, D47 and D65 required for Zn ²⁺ coordination. As the periplasmic Zn ²⁺ -sensor CzcS regulates oprD expression, the interaction with it was analyzed in vitro . Interaction was Zn ²⁺ -dependent, and mutations of D47A or D65A abolished it. We propose a role for PA3962, hereafter periplasmic metallochaperone of YiiP (PmcY), in the context of Zn ²⁺ signaling pathways in P. aeruginosa . The rely YiiP–PmcY, supplies Zn ²⁺ and activates CzcS/CzcR, down-regulating the transcription of the imipenem-permeable OprD. This mechanism would allow P. aeruginosa to put a brake on unspecific mechanisms for micronutrient uptake, with potential xenobiotic entry, while the cytosolic Zn ²⁺ quota is still sufficient.