Recombinant Salmonella phoQ protein

PhoQ is a histidine kinase sensor protein that plays a central role in bacterial signal transduction pathways, particularly in Gram-negative bacteria like *Salmonella enterica* and *Escherichia coli*. It forms a two-component regulatory system with its cognate response regulator, PhoP, to mediate adaptive responses to environmental stresses. PhoQ is activated by extracellular signals such as low magnesium (Mg²⁺) concentrations, acidic pH, and antimicrobial peptides (AMPs) produced by host organisms during infection. Upon activation, it autophosphorylates and transfers the phosphate group to PhoP, which subsequently regulates the expression of genes involved in virulence, membrane remodeling, and resistance to host defense mechanisms.

Structurally, PhoQ consists of a periplasmic sensor domain connected via transmembrane helices to cytoplasmic kinase and regulatory domains. The periplasmic domain detects environmental cues, while the cytoplasmic region orchestrates phosphorylation-dependent signaling. Its ability to sense host-derived AMPs links PhoQ to bacterial pathogenesis, enabling pathogens to modulate their outer membrane composition (e.g., lipid A modifications) to evade immune detection.

Recombinant PhoQ proteins are produced via heterologous expression systems (e.g., *E. coli*) for biochemical and structural studies. These engineered variants allow researchers to dissect PhoQ’s signaling mechanisms, ligand interactions, and regulatory roles. Studies on PhoQ have implications for understanding antibiotic resistance and developing antimicrobial strategies, as disrupting PhoQ/PhoP signaling could attenuate bacterial virulence. Additionally, PhoQ homologs in other pathogens highlight its evolutionary conservation as a key mediator of host-microbe interactions. Research continues to explore its potential as a therapeutic target and a tool for synthetic biology applications.