![[ Tobin R. Sosnick ]](Tobin_Sosnick.jpg) |
Tobin R. SosnickAssistant Professor of the Department of Biochemistry and Molecular Biology, Institute for Biophysical Dynamics.Ph.D. Applied Physics, Harvard Univ. 1989
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Research SummaryThe major goal of our research is to understand how complex biological molecules adopt their functional conformations: "The Protein and RNA Folding Problems". This includes determining the driving forces, sequence of events, and relevant time scales that govern the complicated folding process. We are extending our current research in the active field of protein folding to the relatively unexplored field of ribozyme folding.Our protein folding studies focus on identifying the critical features that guide the early pathway leading to the rate-limiting nucleation event. These studies are primarily conducted with a simple well-defined alpha helical coiled coil GCN4 molecule using rapid mixing (msec) fluorescence and CD spectroscopies. The special capability of isolating on single structure features by site-directed amino acid substitution with coiled coil protein represents a major advance in our ability to dissect and understand the folding process. To further illuminate the nature and structure of the transition state, we are extending typical amino acid mutagenesis by manipulating solvent composition with trifluoroethanol, solvent viscosity, and the D/H isotopic substitution of backbone amides. We are also studying the folding of topologically more complicated proteins, such as lambda repressor, cytochrom c, arc repressor, CI2, IM7, ubiquitin, Protein L, SH3, and Protein G, to test the generalities of our conclusions concerning the folding transition state. To measure the ultimate time-scales in protein folding, we are developing methods to measure microsecond folding rates using a combination of 15N/1H NMR and hydrogen exchange methods. To investigate multiple folding routes in proteins, we have developed a metal ion binding method that can adjust the free energy specifically at one site. Preliminary experiments have been performed on the coiled coil, GCN4. We designed i,i+4 biHis sites and learned about the shape of the folding energy landscape for this model system. We also are studying the thermodynamic and kinetic folding behavior of small and large RNA molecules including ribozymes in collaboration with Prof. Tao Pan. The small system is the well-characterized tRNA, another simple molecule where site-directed modifications can be made and one can hope to learn the fundamental principles of RNA folding. We are also studying the refolding behavior of the multi-domain ribozyme P RNA in order to determine whether the limiting steps in the refolding of larger RNAs are substantially different. An element of these studies is the characterization of the unfolded
state, particularly under physiological conditions from which the refolding
reaction begins, using a combination of biophysical methods including time-resolved
small-angle synchrotron X-ray scattering.
 Some
Selected Papers
Departments & Committees to Which I Belong Department of Biochemistry and Molecular Biology Related Research Topics in Molecular Biosciences |
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