TCBG Seminar

Intermediates and Cooperativity in Single Molecules and Fibers

Professor Norbert Scherer
Department of Chemistry
University of Chicago
Chicago, Illinois

Monday, May 5, 2003
3:00 pm (CT)
3269 Beckman Institute


In contrast to the 2-state folding behavior of small to moderate size proteins, RNA folding is believed to proceed through a (finite) sequence of intermediates. Ensemble experiments on large ribozymes - catalytically active RNAs - indeed indicate multiple transitions. Our new single molecule FRET experiments on a ribozyme from Bacillus subtillis show clear evidence of several intermediates in the equilibrium folding pathway, as a function of [Mg2+]. Information about the dynamics of transitions between the intermediates will be presented. A free energy landscape description of the behavior will be discussed. The second part of the talk will present new single "molecule" studies of large multi-element flagellin fibers from E. coli. Our studies are relevant for elucidating cooperativity in the transition between two flagellar states; the transition behavior having a direct bearing on the motility of E. coli. Force-extension measurements of single bacterial flagella will be presented. We have developed a molecular "sticky slinky" model to extract microscopic interaction strength from the force-extension curves. This and the irreversible work exhibited in the hysteretic extension-retraction curves and differences between the native and mutant phenotypes will be discussed.

Tea and coffee will be served in R3151 Beckman Institute at 2:15pm.

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