F. Jon Kull
Rodgers Professor of ChemistryDean of Graduate Studies
Our laboratory uses biophysical techniques to study protein structure and function. Our primary tool is X-ray crystallography, but we supplement this powerful technique with site-directed mutagenesis, steady state and pre-steady state kinetics, isothermal titration calorimetry, dynamic light scattering and analytical ultracentrifugation. Our goal is to understand at a fundamental level the conformational changes that occur in proteins as they complete the various cellular functions. Armed with this knowledge, we then apply our fundamental understanding of structure/function relationships in order to address the issues of molecular disease. There are currently two major areas of research in the laboratory:
The Mechanism of Motor Protein-based Force Generation
Molecular motor proteins are practically ubiquitous in cellular activities requiring movement, and mutations in motors or defects in motor regulation can have drastic effects. In order to understand the consequences of these defects, we are determining the detailed structural mechanisms employed by cytoskeletal proteins in order to 1) produce directed force along protein filaments and 2) mediate interactions with their various intra- or intermolecular protein targets. For ATP-driven molecular motors, as well as the GTP-driven G-protein family of molecular switches, conformational states are governed by the presence or absence of the nucleotideγ-phosphate. An intriguing question is how such a small conformational change can be sensed by the protein and amplified, sometimes by several orders of magnitude, in order to achieve the various cellular functions of these proteins. We are currently focusing on determining the structures of various unconventional myosins and kinesins, as well as the structures of these motors in complex with their filamentous tracks.
Structural Analysis of Bacterial Virulence Regulators
Vibrio cholerae causes the frequently fatal epidemic diarrheal disease cholera. The expression of its two primary virulence factors, toxin-coregulated pilus and cholera toxin, occurs via a transcriptional cascade involving several activator proteins and serves as a paradigm for the regulation of bacterial virulence. AphA and AphB initiate the expression of the cascade by an as yet not understood synergistic interaction at the tcpPH promoter. ToxT, an AraC-type regulator, then directly activates the promoters of the primary virulence factors. Transcriptional activation at these various promoters occurs only in response to certain environmental stimuli. Such regulation is widespread among bacterial pathogens and allows productive infections to be mounted only in the appropriate biological niches. A fourth protein, HapR is a negative regulator of virulence gene expression that functions to repress expression at the aphA promoter, thereby coordinating quorum sensing regulation with pathogenesis. The long term goals of the work in this project are to understand the molecular basis for this regulation by environmental stimuli so as to facilitate the development of better strategies to prevent and cure bacterial diseases. This project aims to explore the structure/function relationships of four cytoplasmic virulence gene regulator proteins in V. cholerae, AphA, AphB, and ToxT, at their cognate promoters by obtaining high resolution structures of them in the absence and presence of their binding sites. In combination with ongoing mutational studies, the work will significantly increase our understanding of how these proteins activate virulence gene expression, will serve as models for these regulatory protein family members in other bacterial pathogens, and will advance efforts to identify molecules that may function as novel therapeutics.
Sharyn A. Endow, F. Jon Kull and Honglei Liu. (2010)“Kinesins at a glance”. Journal of Cell Science . Oct 15;123(Pt 20):3420-4. PMID: 20930137
Yu Cheng Zhao, F. Jon Kull, Jared C. Cochran.“Modulation of the kinesin ATPase cycle by neck linker docking and microtubule binding”. Journal of Biological Chemistry . Aug 13;285(33):25213-20. PMCID: PMC2919084.
Elisabeth Heuston, C. Eric Bronner, F. Jon Kull and Sharyn A Endow. (2010)“A kinesin motor in a force-producing conformation”. BMC Structural Biology . Jul 5;10:19. PMCID: PMC2906495.
Lowden, M.J., K. Skorupski, M. Pellegrini, M.G. Chiorazzo, R.K. Taylor, and F.J. Kull. (2010) Structure of Vibrio cholerae ToxT reveals a mechanism for fatty acid regulation of virulence genes. Proc. Natl. Acad. Sci. USA . Feb 16;107(7):2860-5. PMCID: PMC284031.
Cochran, J.C., Sindelar, C.V., Mulko, N.K., Collins, K.A., Kong, S.E., Hawley, R.S., and Kull, F.J. (2009) The ATPase Cycle of the Nonmotile Kinesin NOD Allows Microtubule Plus-End Tracking and Drives Chromosome Movement. Cell . Jan 9;136(1):110-22. PMID: 19135893.
Cochran, J.C., and Kull, F.J. (2008) Kinesin Motors: No Strain, No Gain. Cell. Sep 19;134(6):918-9. PMID: 18805085.
De Silva, R.S., Kovacikova, G., Lin, W., Taylor, R.K., Skorupski, K., and Kull, F.J. (2007) Crystal structure of the bacterial virulence gene regulator HapR, J. Bacteriology. Aug;189(15):5683-91.