Acts as an accessory protein in the Cpx two-component envelope stress response system. Binds the periplasmic domain of sensor histidine kinase CpxA, inhibiting induction of the envelope stress response in the absence of inducer. Aids in combating extracytoplasmic protein-mediated toxicity. Homodimer. Interacts with the periplasmic domain of CpxA. Belongs to the CpxP/Spy family. Truncated N-terminus. Truncated N-terminus.