Rodney K. Tweten, Ph.D.
OU Presidential Professor
George Lynn Cross Research Professor

Doctoral Training: 1982, Kansas State University
Postdoctoral Training: University of California , Los Angeles

Research Emphasis: Structural biology and biochemistry of bacterial protein toxins.

Email: Rod-Tweten@ouhsc.edu
Phone: (405) 271-1205

Tour Dr. Tweten's Lab

Tweten's Lecture Slides

 

The primary focus of our research is the study of the mechanisms of cytolytic toxins from various bacterial species. My lab group primarily studies the cholesterol dependent cytolysins (CDCs) from various pathogenic bacteria. An intriguing characteristic of these toxins, which appears to be repeated in many membrane penetrating bacterial toxins, is the ability of these soluble, monomeric proteins to make the transition to a homo-oligomeric pore-forming complex on the membrane of eukaryotic cells. We use fluorescence spectroscopy to map functional domains and the structural transitions of these toxins as they make the transition from a soluble monomeric state to a membrane bound oligomeric pore. Fluorescent probes are targeted to specific sites of the toxin molecule by the placement of unique cysteine residues in the toxin structure via in vitro mutagenesis. The probes are then used to follow the transitions that the various domains of the toxin undergo during membrane interaction. A significant amount of data can be obtained from the various measurable characteristics of these probes (i.e., intensity, lifetime, anisotropy, dynamic anisotropy, etc) that can provide evidence as to the environment of that probe and therefore the environment of the residue of the toxin. These studies are part of an ongoing collaborative effort with Dr. Art Johnson of Texas A&M University.

 

 

Spacefilling Crystal Structure of Perfringolysin O

The CDCs are produced by and contribute to the pathogenic mechanisms of a wide variety of Gram-positive bacterial pathogens and so the study of the CDCs (formerly the thiol-activated or oxygen labile toxins) is of considerable interest. The CDCs contribute to the pathogenic mechanisms of these pathogens in unique ways that is strongly associated with their pore-forming mechanism. Our studies span many structure-function aspects of these toxins from the mechanism of receptor interaction to the formation of the pore and the effect they have on eukaryotic cell biology. The CDCs have undergone interesting evolutionary changes, depending on the pathogen that produces it. Although the CDCs have all retained their ability to produce large pores in the membrane of eukaryotic cells, they have diverged in ways that have changed how they contribute to the pathogenic mechanism of a specific pathogen. For instance, streptolysin O (SLO) has evolved to function as a protein translocation channel changed, whereas intermedilysin has change such that it binds to a unique receptor, human CD59, a late stage complement inhibitor. Listeriolysin O exhibits a pH-dependent mechanism that is important to its ability to facilitate the escape of Listeria monocytogenes, an facultative intracellular pathogen, from the phagosome. Streptococcus pneumoniae produces pneumolysin which also exhibits the ability to fix complement in the host, thus depleting this antibacterial system. Hence, the CDC structure has undergone many interesting permutations that appear to complement the pathogenic mechanism of a particularly bacterial pathogen.

The study of toxin mechanisms and their effect on the mammalian cell has led us into a wide variety of research topics that span infectious disease to the re-engineering of toxins to target cancer cells.

 

Selected Publications

1.         Soltani, C. E., E. M. Hotze, A. E. Johnson, and R. K. Tweten. 2007. Specific protein-membrane contacts are required for prepore and pore assembly by a cholesterol-dependent cytolysin. J. Biol. Chem . in press.

2.         Rossjohn, J., G. Polekhina, S. C. Feil, C. J. Morton, R. K. Tweten, and M. W. Parker. 2007. Structures of Perfringolysin O Suggest a Pathway for Activation of Cholesterol-dependent Cytolysins. J Mol Biol.

3.         Melton, J. A., L. M. Bentsen, and R. K. Tweten. 2006. Mutational analysis of Clostridium septicum alpha toxin reveals residues critical for receptor-binding, oligomerization and control of membrane insertion. Biochemistry in press.

4.         Tweten, R. K. 2005. The cholesterol-dependent cytolysins; a family of versatile pore-forming toxins. Infect Immun 73:6199-6209.

5.         Schuerch, D. W., E. M. Wilson-Kubalek, and R. K. Tweten. 2005. Molecular basis of Listeriolysin O pH-dependence. Proc Natl Acad Sci 102:12537–12542

6.         Ramachandran, R., R. K. Tweten, and A. E. Johnson. 2005. The domains of a cholesterol-dependent cytolysin undergo a major FRET-detected rearrangement during pore formation. Proc Natl Acad Sci 102:7139-7144.

7.         Polekhina, G., K. S. Giddings, R. K. Tweten, and M. W. Parker. 2005. Insights into the action of the superfamily of cholesterol-dependent cytolysins from studies of intermedilysin. Proc Natl Acad Sci 102:600-605.

8.         Giddings, K. S., A. E. Johnson, and R. K. Tweten. 2005. Perfringolysin O and intermedilysin: mechanisms of pore formation by the cholesterol-dependent cytolysins, p. 669-677. In J. E. Alouf and M. R. Popoff (ed.), Bacterial Toxins:  A Comprehensive Sourcebook, 3 ed. Academic Press, London.

9.         Ramachandran, R., R. K. Tweten, and A. E. Johnson. 2004. Membrane-dependent conformational changes initiate cholesterol-dependent cytolysin oligomerization and intersubunit b-strand alignment. Nat Struct Mol Biol 11:697-705.

10.       Melton, J. A., M. W. Parker, J. Rossjohn, J. T. Buckley, and R. K. Tweten. 2004. The identification and structure of the membrane-spanning domain of the Clostridium septicum alpha toxin. J Biol Chem 279:14315-14322.

11.       Giddings, K. S., J. Zhao, P. J. Sims, and R. K. Tweten. 2004. Human CD59 is a receptor for the cholesterol–dependent cytolysin intermedilysin. Nat Struct Mol Biol 12:1173-1178.

12.       Czajkowsky, D. M., E. M. Hotze, Z. Shao, and R. K. Tweten. 2004. Vertical collapse of a cytolysin prepore moves its transmembrane β-hairpins to the membrane. EMBO J 23:3206-3215.

13.       Heuck, A. P., R. K. Tweten, and A. E. Johnson. 2003. Assembly and topography of the prepore complex in cholesterol-dependent cytolysins. J Biol Chem 278:31218–31225.

14.       Giddings, K. S., A. E. Johnson, and R. K. Tweten. 2003. Redefining cholesterol's role in the mechanism of the cholesterol-dependent cytolysins. Proc Natl Acad Sci U S A 100:11315-11320.

15.       Ramachandran, R., A. P. Heuck, R. K. Tweten, and A. E. Johnson. 2002. Structural insights into the membrane-anchoring mechanism of a cholesterol-dependent cytolysin. Nat Struct Biol 9:823-7.

16.       Hotze, E. M., A. P. Heuck, D. M. Czajkowsky, Z. Shao, A. E. Johnson, and R. K. Tweten. 2002. Monomer-monomer interactions drive the prepore to pore conversion of a beta-barrel-forming cholesterol-dependent cytolysin. J Biol Chem 277:11597-605.

17.       Hotze, E. M., E. M. Wilson-Kubalek, J. Rossjohn, M. W. Parker, A. E. Johnson, and R. K. Tweten. 2001. Arresting pore formation of a cholesterol-dependent cytolysin by disulfide trapping synchronizes the insertion of the transmembrane beta-sheet from a prepore intermediate. J Biol Chem 276:8261-8.