title: Mapping backbone and side-chain interactions in the transition state of a coupled protein folding and binding reaction.
abstract: Understanding the mechanism of protein folding requires a detailed knowledge of the structural properties of the barriers separating unfolded from native conformations. The S-peptide from ribonuclease S forms its α-helical structure only upon binding to the folded S-protein. We characterized the transition state for this binding-induced folding reaction at high resolution by determining the effect of site-specific backbone thioxylation and side-chain modifications on the kinetics and thermodynamics of the reaction, which allows us to monitor formation of backbone hydrogen bonds and side-chain interactions in the transition state. The experiments reveal that α-helical structure in the S-peptide is absent in the transition state of binding. Recognition between the unfolded S-peptide and the S-protein is mediated by loosely packed hydrophobic side-chain interactions in two well defined regions on the S-peptide. Close packing and helix formation occurs rapidly after binding. Introducing hydrophobic residues at positions outside the recognition region can drastically slow down association.
authors.affiliation: Munich Center for Integrated Protein Science and Department of Chemistry, TU München, Lichtenbergstrasse 4, D-85747 Garching, Germany.
authors.forename: Annett
authors.initials: A
authors.lastname: Bachmann
authors.forename: Dirk
authors.initials: D
authors.lastname: Wildemann
authors.forename: Florian
authors.initials: F
authors.lastname: Praetorius
authors.forename: Gunter
authors.initials: G
authors.lastname: Fischer
authors.forename: Thomas
authors.initials: T
authors.lastname: Kiefhaber
mesh_terms: D006860:Hydrogen Bonding; D007700:Kinetics; D008958:Models, Molecular; D011485:Protein Binding; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D011506:Proteins