CpxA_peri is the periplasmic domain-family of the Gram-negative Gammaproteobacteria two-component signalling system, Cpx. It represents the recognition-site for sensing specific envelope stress signals. The fold that the domain-core of CpxA_peri conforms to is a PAS fold. The domain senses the environmental change and triggers a signal transduction to the cytoplasmic domain. As well as the PAS-core, there is a C-terminal tail that is necessary for ligand-sensing and binding to CpxP, a CpxA-associated and a regulatory protein [1]. This domain recognises KCl and RbCl (Matilla et. al., FEMS Microbiology Reviews, fuab043, 45, 2021, 1. https://doi.org/10.1093/femsre/fuab043).

1: The crystal structure of the periplasmic domain of Vibrio parahaemolyticus CpxA. Kwon E, Kim DY, Ngo TD, Gross CA, Gross JD, Kim KK; Protein Sci. 2012;21:1334-1343. PMID:22760860