C. BUSTAMANTE - Use of Crooks Fluctuation Theorem to Study the Interdomain Folding Cooperativity of a Protein

• Coloquios

Seminario en el DF:

Carlos Bustamante.

University of California, Berkeley, USA.

Martes 13/5/2014, 10 hs.
 Aula Seminario, 2do piso, Pabellón I.  

Resumen:

Proteins are complex functional molecules that tend to segregate into structural regions. Throughout evolution, biology has harnessed this modularity to carry out specialized roles and regulate higher-order functions such as allostery. Cooperative communication between protein regions is important for catalysis, regulation, and efficient folding. However, how domains communicate and contribute to a protein’s energetics and folding is still poorly understood. Bulk methods rely on a simultaneous and global perturbation of the system and can miss potential intermediates, thereby overestimating protein cooperativity and domain coupling. To overcome this problem we used single molecule manipulation methods (optical tweezers or AFM) to mechanically induce the selective unfolding of particular regions of a single protein while monitoring the response of other regions not directly affected by the external force. We applied one of the newly derived fluctuation theorems (Crook’s theorem) that allows to extract equilibrium thermodynamic information from the irreversible work done on a system. In this way we evaluate the cooperativity between domains by determining the unfolding energy of topological variants pulled along different directions. We show that topology of the polypeptide chain critically determines the folding cooperativity between domains, and what parts of the folding/unfolding landscape are explored. We speculate that proteins may have evolved to select certain topologies that increase coupling between regions to avoid areas of the landscape that lead to kinetic trapping and misfolding.