F. Jon Kull
Associate Professor of Chemistry
Professor Kull received his A.B. degree in chemistry and biology in 1988 from Dartmouth College. He received a Ph.D. in biochemistry in 1996 from the University of California, San Francisco. In 1998, following a postdoc at the Howard Hughes Medical Institute in San Francisco, he moved to the Department of Biophysics at the Max-Planck Institute for Medical Research in Heidelberg, Germany. He joined the Dartmouth faculty in Fall 2001.
Research Interests
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 three major areas of research in the laboratory:
Project 1: The mechanism of motor protein-based force generationMolecular 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 nucleotide γ-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.
Project 2: Biochemical and structural analysis of dynamin
The dynamin protein family consists of large GTPases involved in functions such as endocytosis, vesicle trafficking, maintenance of mitochondrial morphology, and viral resistance. Although there is evidence that dynamin drives membrane fission via a force-generating mechanism, there is much debate as to whether it actively generates force, or rather acts a regulator of endocytosis. In order to determine how dynamins function, we have solved the crystal structures of the GTPase domain of both rat and Dictystelium dynamin, providing the first atomic-level picture of a dynamin family protein. We have also crystallized a full-length mammalian dynamin and are in the process of solving its structure. In the future we plan to identify and structurally characterize dynamin mutants, as well as dynamin binding and regulatory proteins. Our goals for this project are to answer three major questions: 1) What structural features enable dynamin to form polymeric rings around the necks of endocytotic vesicles? 2) What is the structural basis for regulation of dynamin's GTPase activity? 3) What conformational changes take place in dynamin as it cycles through its GTP hydrolysis cycle?
Project 3. 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.
