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Physics Colloquium – Victor Muñoz
April 12 @ 3:30 pm - 4:30 pm
Victor Muñoz, University of California-Merced
Lessons About Biomolecular Rate Theory from Ultrafast Kinetics and Single-Molecule Spectroscopy of Fast-Folding Proteins
Natural proteins fold and unfold with rates that define their biological properties and vary vastly from protein to protein. Understanding how these rates are determined is essential to decipher the mechanisms of protein folding, but is also a convenient system to explore the fundamental aspects of biomolecular rate theory. Protein (un)folding rates are described as diffusion on a free energy surface obtained by projecting the protein-solvent hyper-dimensional phase space (or folding energy landscape) onto one or few order parameters that capture the reaction’s progress. Such description often reduces to Kramers rate theory, in which the rates depend on the free energy barrier separating the native and unfolded states and a prefactor term that sets the timescale for crossing such barrier or folding speed limit. A pervasive problem in the field has been the impossibility to extricate these two factors from experimentally measured folding and unfolding rates. However, recent work in the biophysical characterization of ultrafast protein folding and technical advances in single-molecule fluorescence and force spectroscopy are providing first direct glimpses of the (un)folding transition paths (the reactive barrier crossing events) undertaken by individual protein molecules and how they connect to the free energy barrier.
In my talk, I will review some of our recent results in this area that shed new light onto the mechanisms of protein folding and provide useful tests of the applicability of Kramers rate theory to biomolecular processes.