Post Doctoral Fellows
The major invasive fungal pathogens (Candida albicans, Aspergillus species and Cryptococcus species) require an intact trehalose biosynthesis pathway for virulence. However, there are currently no known antifungal agents that target the trehalose pathway. Additionally, the few inhibitors of the trehalose pathway that have been identified have low potency. Therefore, there is a need to identify effective inhibitors against the fungal trehalose biosynthesis pathway as a key first step towards the development of new antifungal drugs. My research goals are to identify novel inhibitors of trehalose biosynthesis by determining the structure and function of trehalose biosynthesis enzymes.
Neisseria gonorrhoeae is a strict human pathogen and the sole causative agent of the sexually transmitted disease gonorrhea. Alarmingly, antibiotic resistant gonorrheae has been emerging, generating a need to understand the proteins that play a role in neisserial survival. A major threat to survival is oxidative stress from the immune system, commensal organisms, and respiration. I seek to analyze the oxidative stress sensing transcriptional regulators NmlR, MtrR, and ng1427 to determine the structural and biochemical basis for neisserial response and survival to oxidative stress.
Cryptococcus infection has become one of the leading causes of death among immunocompromised people around the world. It has been found that trehalose is very essential for Cryptococcus to maintain its virulence. Disruption of trehalose synthesis pathway reduces or even abolishes the virulence of Cryptococcus in rabbits, conferring this pathway a very good antifungal drug target.Therefore, my research is to understand the structural and biochemical characterizations proteins involved in this pathway.
The pathogenicity of Francisella tularensis stems from its pathogenicity island (FPI). The alarmone ppGpp coordinates the transcription of genes associated with the stringent response in F. tularensis , and specifically, genes located in the FPI. I want to understand the pathway by which ppGpp effectively coordinates F. tularensis pathogenic actions - such as phagosomal escape and intracellular replication of the bacterium - through regulation of the FPI.
Tien Jui Yen
Bacillithiol (BSH), recently identified as the major low molecular weight thiol in Gram-positive bacteria Firmicutes, is proposed to be the functional alternative for glutathione as the redox buffer and antioxidant. My thesis project aims to understand the molecular mechanisms of how BSH mediates redox homeostasis. By taking advantage of X-ray crystallography and biochemistry, we focus on (1) the regulatory mechanism of BSH biosynthesis by structural characterization of the essential enzyme involved in BSH biosynthesis; (2) the physiological role of BSH in redox signaling under oxidative stress through BSH-mediated disulfide bond modification of redox sensor proteins. Due to the presence of significant pathogens in Firmicutes, such as S. aureus and B. anthracis, these studies can further provide potential targets for future drug design to treat BSH-containing bacteria.
I am working to structurally and biochemically characterize a toxin-antioxin pair whose expression has been shown to be upregulated in drug-tolerant persistant populations of Mycobacterium tuberculosis. Latent infection due to persister cell populations remains a major obstacle in the treatment of tuberculosis and other bacterial infections. Our studies on this protein pair will help to elucidate the molecular mechanisms that drive the formation of persisters.
HipA is a known factor mediating multidrug tolerance and persistence in E. coli and a recent collaborative study between the Schumacher and Brennan laboratories has shown that this protein-serine kinase appears to play a significant role in some chronic infections such as those of the urinary tract. Using Fluorescence Linked Enzyme Chemoproteomic Strategy (FLECS), a technique developed by the Haystead Laboratory here at Duke University, I seek to identify ATP-competitive kinase inhibitors that show potential to reduce or eliminate HipA activity. This technique, along with structure-based optimization, will hopefully lead to a highly specific drug that eliminates the effect of HipA on multidrug tolerance and persistence.
Treatment of infections caused by Staphylococcus aureus, a Gram-positive bacterium that can lead to pneumonia, endocarditis, sepsis and toxic shock syndrome, is becoming increasingly compromised by the emergence of multidrug resistance in clinical isolates. Of interest is the regulation of the multidrug efflux pump MepA, which promotes multidrug resistance of S. aureus by pumping out a variety of structurally and chemically distinct antibiotics. I study MepR, a member of the MarR family member that represses the mepA gene but is induced upon binding the same cationic, lipophilic cytotoxins that are substrates of MepA. Hence, MepR acts a cellular cytotoxin sensor. I aim to structurally and biochemically characterize the substrate-binding site of MepR and analyze the mechanism by which drug binding prevents MepR binding to DNA.
I am a senior, majoring in Biology with a Cell and Molecular Biology concentration. My primary focus has been on bacterial multi-drug tolerance, which is largely responsible for chronic infections. In E. coli, the HipBA toxin-antitoxin system has been shown to be involved in the formation of persister cells, which exhibit multi-drug tolerance. Currently, I am working on a project to help characterize HipA autophosphorylation, a process that is vital for bringing about bacterial persistence.