How Regulated Proteolysis Controls Bacterial Virulence

PROJECT SUMMARY All pathogens require proteins to cause disease. Protein abundance reflects a delicate balance between synthesis and degradation critical for pathogenesis and antibiotic tolerance. Protein degradation must be tightly controlled because its effects are irreversible. We aim to determine how related bacterial species, including the human gastroenteritis- and murine typhoid-causing Salmonella enterica serovar Typhimurium, deploy proteolysis as an essential virulence strategy. We will investigate how the master virulence regulator PhoP controls the abundance, activity, or specificity of all five ATP-dependent proteases: Lon, HslUV, ClpAP, ClpXP, and FtsH. We will examine how the PhoP antagonist EIIANtr is proteolyzed in a phoP- and lon-dependent manner and identify the role that proteolysis of PhoP and EIIANtr plays in the expression kinetics of virulence genes when bacteria are inside macrophages. We will uncover proteins and behaviors controlled by the poorly understood virulence-promoting protease HslUV; critically test the role that proteolysis of gene silencer H-NS plays in expression of foreign genes; and solve the mechanism(s) by which protease adaptors prevent protein degradation during infection. We will identify the signals governing expression of virulence proteins CspI and IraP via their 5' leader mRNAs and define the domain(s) of the virulence protein MgtB mediating growth in very low Mg2+ and survival in Slc11a1+/+ macrophages. The proposed research program takes a comprehensive approach, including technical and conceptual innovations, to reveal significant, broadly applicable principles in bacterial physiology and pathogenesis and new therapeutic interventions that overcome antibiotic resistance.