Small proteins in bacterial signaling network

Our group focuses on the small proteins that involved in bacterial signaling. Specifically, we are interested in the regulation of the PhoQ/PhoP two-component system (TCS) by two small proteins, MgrB and SafA. The PhoQ/PhoP system is essential for magnesium homeostasis, host adaptation and virulence in enterobacteria. PhoQ senses host-associated stimuli including low magnesium, low pH, cationic antimicrobial peptides and osmotic upshift. The activated PhoQ sensor kinase autophosphorylates and then transfers the phosphate group to its cognate response regulator PhoP. The response regulator subsequently binds to specific gene promoters to regulate their expression, thus initiating cellular responses to environmental changes.

Overview of the PhoQ/PhoP two-component system in E. coli and Salmonella. PhoQ (shown in blue-green ribbon) directly senses environmental stimuli, which include magnesium limitation, low pH, antimicrobial peptides and osmotic upshift, and activates PhoP by phosphorylation. This activation can be regulated by the small proteins MgrB and SafA, which inhibit and activate PhoQ kinase activity, respectively. SafA connects PhoQ/PhoP with EvgS/EvgA, which is a two-component system activated by low pH combined with the presence of Na+ or K+. The phosphorylated PhoP promotes the expression of a set of genes that can be grouped into six categories. — Overview of the PhoQ/PhoP two-component system in *E. coli* and *Salmonella.* PhoQ (shown in blue-green ribbon) directly senses environmental stimuli, which include magnesium limitation, low pH, antimicrobial peptides and osmotic upshift, and activates PhoP by phosphorylation. This activation can be regulated by the small proteins MgrB and SafA, which inhibit and activate PhoQ kinase activity, respectively. SafA connects PhoQ/PhoP with EvgS/EvgA, which is a two-component system activated by low pH combined with the presence of Na⁺ or K⁺. The phosphorylated PhoP promotes the expression of a set of genes that can be grouped into six categories.

Overview of the PhoQ/PhoP two-component system in *E. coli* and *Salmonella.* PhoQ (shown in blue-green ribbon) directly senses environmental stimuli, which include magnesium limitation, low pH, antimicrobial peptides and osmotic upshift, and activates PhoP by phosphorylation. This activation can be regulated by the small proteins MgrB and SafA, which inhibit and activate PhoQ kinase activity, respectively. SafA connects PhoQ/PhoP with EvgS/EvgA, which is a two-component system activated by low pH combined with the presence of Na⁺ or K⁺. The phosphorylated PhoP promotes the expression of a set of genes that can be grouped into six categories.

Two small proteins MgrB and SafA regulate the PhoQ/PhoP TCS by directly interacting with PhoQ. MgrB inhibits, while SafA activates PhoQ kinase activity. We investigate their regulations by monitoring PhoQ/small protein interactions, following signal integrations, identifying functionally important residues, mapping binding surfaces, and consequently designing peptide inhibitors to suppress bacterial virulence. Furthermore, we will identify other protein targets of MgrB and SafA and find out how small proteins connect different TCSs. To explore the mostly underinvestigated research field of small proteins, we use a collection of experimental approaches including FRET, microscopy, FACS analysis, genetics, proteomics, standard molecular biology techniques as well as simulations and crystallography via collaborations.