The PhoQ Sensor is required for the virulence of various Gram-negative bacteria by allowing interaction of PhoPQ with the intracellular membrane, resulting in remodelling of the bacterial cell surface and subsequent bacterial resistance to host antimicrobial peptides. The domain contains a major flat acidic surface, which binds to at least 3 calcium ions, neutralising the domain's negative charge and allowing interaction with the negatively charged membrane [1]. This domain recognises divalent metal cations, and antimicrobial cationic peptides (Matilla et. al., FEMS Microbiology Reviews, fuab043, 45, 2021, 1. https://doi.org/10.1093/femsre/fuab043).

1: Metal bridges between the PhoQ sensor domain and the membrane regulate transmembrane signaling. Cho US, Bader MW, Amaya MF, Daley ME, Klevit RE, Miller SI, Xu W; J Mol Biol. 2006;356:1193-1206. PMID:16406409