Hoffman, Paul S.
Professor Emeritus, Medicine: Infectious Diseases and International Health
- BS, Biology, Virginia Polytechnic Institute and State University
- MS, Bacteriology, Iowa State University
- PhD, Microbiology, Virginia Polytechnic Institute and State University
Molecular mechanisms of microbial pathogenesis and antibiotic development
My research program focuses on molecular mechanisms of microbial pathogenesis by Legionella pneumophila (the agent of Legionnaires' disease) and the stomach ulcer causing bacterium Helicobacter pylori. Legionella pneumophila is an intracellular parasite of fresh water amoeba that when transmitted by aerosol to humans often causes severe pneumonia. We discovered that DsbA2 is a novel periplasmic disulfide bond oxidoreductase that catalyzes both the formation of disulfide bonds and corrects disulfide bonding mistakes to aid protein folding that are important in the assembly of macromolecular structures. This new family of bifunctional proteins is required for the proper formation and function of Type IV secretion virulence systems (T4SS) in many intracellular pathogens. Many of these pathogens, like L. pneumophila, are dimorphic and display a developmental cycle that ends in formation of infectious cyst-like forms that are important in transmission of disease. We hypothesize that L. pneumophila cysts are pre-programmed to activate their T4SS following contact with a suitable host cells and that DsbA2 delivers reducing equivalents to activate the Dot/Icm T4SS of L. pneumophila. Legionella is a model system for the study of obligate intracellular pathogens such as Chlamydia and Coxiella.
Helicobacter pylori colonizes the gastric mucosa of humans, a niche that is hostile to other microbes. In the absence of niche competition, how much regulation does a microbe need? We and others have shown that H. pylori contains few transcription factors and that regulation is not a strong on/off, as seen with regulators in E. coli. There are two essential transcription factors ArsR and HP1043 and while ArsR is associated with responses to acid, the function of HP1043 is unknown. Our studies connect HP1043 to oxidative stress and to redox toxicity of prodrugs like metronidazole. Using proteomics and qPCR techniques, we have identified members of the HP1043 regulon using a mutant form of the protein. We have also identified a non-coding regulatory RNA upstream of HP1043 that cooperates with HP1043 in regulating many genes of the regulon. These ncRNAs are abundant in H. pylori and appear to be important in modulating expression of many gene systems.
My laboratory has been involved in the study of drug resistance and in the development of new genomic/ bioinformatic based strategies for identifying new microbial targets to aid the discovery of new therapeutics. We have synthesized a novel antibiotic Amixicile that is a potent inhibitor of pyruvate ferredoxin oxidoreductase (PFOR) and related alpha keto acid decarboxylases common to all strictly anaerobic bacteria, anaerobic human parasites and to microaerobic human pathogens Helicobacter pylori and Campylobacter jejuni. The target is not found in humans or probiotic beneficial microorganisms. Amixicle shows efficacy against Clostridium difficile and Helicobacter pylori in mouse infection models. Related analogues with different chemistries show efficacy against biofilm producing bacteria and against Legionella pneumophila, Bacillus anthracis and MRSA strains of Staphylococcus aureus.