Professor, Department of Microbiology and Molecular Genetics
Education & Training
- Postdoctoral Fellow
- University of Chicago
- University of California, Los Angeles, 2000
Dr. Ton-That obtained his Ph.D. degree from the University of California at Los Angeles (UCLA) in 2000, working with Dr. Olaf Schneewind to elucidate the mechanism of sortase-catalyzed cell wall anchoring of surface proteins in Staphylococcus aureus. He came to the University of Chicago for his postdoctoral training and became interested in pilus assembly in Gram-positive bacteria. Between 2004 and 2008, he held an assistant professor position at the University of Connecticut Health Center to continue his studies of Gram-positive pili and their role in biofilm formation and bacterial pathogenesis. In 2009, he joined the Department of Microbiology and Molecular Genetics at the University of Texas-Houston Medical School. His research program currently focuses on the molecular assembly on the cell surface of Gram-positive pathogens, oxidative protein folding in Gram-positive bacteria, and virulence mechanisms of the Gram-negative pathogen Fusobacterium nucleatum. His teaching duties include courses for graduate and medical students and directing a laboratory-based course in fluorescence and electron microscopy.
Molecular Mechanisms of Bacterial Pathogenicity
Four major projects are being investigated in the laboratory with the long term goal of elucidating molecular mechanisms of pathogenicity by Gram-negative and Gram-positive pathogens. We employ a multidisciplinary approach combining classical and modern techniques, which include genetics, various biochemical methods, electron microscopy, electron cryo-tomography, X-ray crystallography, biophysics, mass spectrometry, cell-based assays, and rodent models of infection.
1. Molecular assembly on the cell surface of Gram-positive bacteria
Gram-positive pathogens assemble on their surface covalently linked protein polymers known as pili or fimbriae that enable these bacteria to adhere to specific host tissues and initiate a pathogenic program. A typical pilus contains a major pilin forming the shaft and one or more minor pilin subunits. The heteromeric pilus is assembled by tandem transpeptidase enzymes called sortases. A pilus-specific sortase catalyzes the extension of pilus heteropolymers. The product of this cyclic polymerization is handed directly to the housekeeping sortase SrtA, which completes the assembly process by anchoring the resulting pilus polymer to the bacterial peptidoglycan. Several aspects of this biphasic mode of pilus assembly are not well understood. The current interests of the lab are to (a) uncover the essential function and regulation of sortase SrtA in cell surface homeostasis in the oral pathogen Actinomyces oris, (b) dissect the molecular interactions of pilins and non-pilin surface proteins with various cellular receptors, and (c) elucidate the mechanism of pilus hijacking of a coaggregation factor. Furthermore, the commonality of these aspects is also being examined in Corynebacterium diphtheriae, Enterococcus faecalis, and Streptococcus agalactiae (group B Streptococcus, GBS).
2. Post-translocational protein folding in Gram-positive bacteria
Many virulence determinants including pili and toxins are translocated across the cytoplasmic membrane by the Sec translocon in an unfolded state. How these proteins are maintained in a native state after translocation is not well understood in Gram-positive bacteria. We propose that the Gram-positive Actinobacteria employ a pair of membrane-bound oxidoreductase enzymes termed MdbA/MbdB as a general oxidative protein folding machine. The current focus of the lab is to elucidate this mechanism of oxidative protein folding in A. oris, to determine the conservation of this pathway in other Gram-positive bacteria, and to explore preventive strategies for dental caries and bacterial infections.
3. Development of a cell-based assay to discover new bacterial anti-infective agents
In collaboration with Dr. Robert Clubb at UCLA, we will develop and implement a novel, cell-based assay to discover small molecules that disrupt the attachment of virulence factors to the Gram-positive bacterial cell wall. The assay will be used to discover protein display inhibitors that target Staphylococcus aureus, a leading cause of lethal hospital- and community-acquired infections in the United States, as well as many other Gram-positive pathogens. The assay exploits our recent discovery that growth of A. oris depends on the activity of its sortase enzyme.
4. Virulence determinants of Fusobacterium nucleatum
The Gram-negative pathogen Fusobacterium nucleatum is a key colonizer in the development of oral biofilms and well known for its association with human diseases including oral infections, preterm birth, and colorectal cancer. F. nucleatum has an inherent ability to interact with many early and late colonizers of the oral biofilms. It induces inflammatory responses and preterm birth in rodent models of infection, as well as promoting colorectal carcinogenesis in vivo. Despite its pathogenic potential, we have limited knowledge about the mechanisms of fusobacterial virulence and associated factors. A major obstacle limiting progress is the lack of robust genetic tools and systematic investigations. We have begun to tackle this problem with our multiple complementary approaches including forward and reverse genetics, cryo-electron tomography, biochemical methods, and rodent models of infection. We are currently characterizing novel factors and pathways resulted from these experimental approaches that affect bacterial virulence and fitness.
- Sanchez B, Chang C, Wu C, Tran B, and Ton-That H (2017). Electron transport chain is biochemically linked to pilus assembly required for polymicrobial interactions and biofilm formation in the Gram-positive actinobacterium Actinomyces oris. mBio, (In Press).
- Luong TT, Reardon-Robinson ME, Siegel SD, Ton-That H (2017). Reoxidation of the Thiol-Disulfide Oxidoreductase MdbA by a Bacterial Vitamin K Epoxide Reductase in the Biofilm-forming Actinobacterium Actinomyces oris. Journal of Bacteriology, 199(10).pii: e00817-16.
- Siegel SD, Wu C, and Ton-That H (2016). A type I signal peptidase is required for pilus assembly in the Gram-positive biofilm-forming bacterium Actinomyces oris. Journal of Bacteriology, 198(15):2064 –2073.
- Siegel SD, Liu J, and Ton-That H (2016). Biogenesis of the Gram-positive bacterial cell envelope. Current Opinion in Microbiology, 34:31–37.
- Reardon-Robinson ME, Osipiuk J, Jooya N, Chang C, Joachimiak A, Das A, and Ton-That H (2015). A thiol-disulfide oxidoreductase of the Gram-positive pathogen Corynebacterium diphtheriae is essential for viability, pilus assembly, toxin production and virulence. Molecular Microbiology, 98(6):1037-50.
Graduate Research Assistant: Available
Graduate Research Assistant positions are available in the Ton-That Lab to investigate the molecular mechanisms of bacterial pathogenicity. Thesis projects will be centered on the four major projects in the lab, which include “Molecular assembly on the cell surface of Gram-positive bacteria”, “Post-translocational protein folding in Gram-positive bacteria”, “Development of a cell-based assay to discover new bacterial anti-infective agents”, and “Virulence determinants of Fusobacterium nucleatum”. The laboratory employs a multidisciplinary approach that combines genetics, molecular biology, electron microscopy, X-ray crystallography, biophysics, mass spectrometry, and various biochemical methods, as well as cell-based assays and rodent models of infection. Thus, graduate students will have ample opportunities to be broadly trained. Please contact Dr. Hung Ton-That (email@example.com) for lab rotations if interested.