Current Research
Metallostasis: Transition metal homeostasis in bacterial pathogens (project 1)
In this project, our goal is to understand the molecular mechanisms of how cells regulate the intracellular bioavailability of essential transition metal ions, notably Cu, Mn and Zn among others. This process, termed metal homeostasis and resistance, represents an important battleground in human host-bacterial pathogen interactions since these ions may be limiting or in excess, both detrimental to the survival of the invading microbe. Metal sensor proteins bind specific DNA sequences and regulate the expression of homeostasis genes in response to specific metal ions. Published studies involve the use of ion mobility mass spectrometry and methyl-NMR dynamics approaches to elucidate mechanisms of allosteric regulation in metallosensors, and understanding the physiological response of Acinetobacter baumanni to host-imposed Zn limitation, Fe limitation and Mn toxicity in Streptococcus pneumoniae using a variety of bioanalytical approaches. Much recent work has focused on obtaining new structural and biochemical insights into GTP- and ATP-hydrolysis powered “metallochaperones” that are activated by the transition metal starvation response in all kingdoms of life.
Persulfide sensing and reactive sulfur species (RSS) in bacteria (project 2)
In this project, we are developing new concepts of bacterial hydrogen sulfide (H2S) homeostasis, and seeking an understanding of the chemistry and physiological adaptation of H2S misregulation in important microbial pathogens. In 2014, we discovered a paralog of a copper-sensing operon repressor CsoR in Staphylococcus aureus that we coined CstR, for CsoR-like sulfurtransferase repressor. CstR senses reactive sulfur species (RSS), including inorganic and organic low molecular weight (LMW) thiol persulfides, that result from the effects of sulfide stress, resulting in induction of the cst operon. Our published work in selected firmicutes and in Gram-negative bacteria (Rhodobacter, Acinetobacter spp.) reveals that RSS sensing and hydrogen sulfide homeostasis is more widespread than previously thought. We discovered orthogonal chemistries of two RSS-inducible enzymes that clear RSS and developed quantitative RSS profiling and a global proteomics workflow to detect S-sulfuration in bacteria. Current work is focused on the structural biology of RSS clearance systems and the deleterious impact of over-persulfidation in cells.
Metallostasis and H2S/RSS homeostasis are linked by the LMW thiol pool foundational to cellular redox and transition metal buffering, cysteine thiol chemistry, and iron-sulfur (Fe-S) protein biogenesis. Recent work suggests that a new (yet old!) LMW thiol/thione, L-ergothioneine, may be widespread in firmicutes, and is the “glue” that bridges both projects.