title: Thermodynamics of folding, stabilization, and binding in an engineered protein--protein complex.
abstract: We analyzed the thermodynamics of a complex protein-protein binding interaction using the (engineered) Z(SPA)(-)(1) affibody and it's Z domain binding partner as a model. Free Z(SPA)(-)(1) exists in an equilibrium between a molten-globule-like (MG) state and a completely unfolded state, wheras a well-ordered structure is observed in the Z:Z(SPA)(-)(1) complex. The thermodynamics of the MG state unfolding equilibrium can be separated from the thermodynamics of binding and stabilization by combined analysis of isothermal titration calorimetry data and a separate van't Hoff analysis of thermal unfolding. We find that (i) the unfolding equilibrium of free Z(SPA)(-)(1) has only a small influence on effective binding affinity, that (ii) the Z:Z(SPA)(-)(1) interface is inconspicuous and structure-based energetics calculations suggest that it should be capable of supporting strong binding, but that (iii) the conformational stabilization of the MG state to a well-ordered structure in the Z:Z(SPA)(-)(1) complex is associated with a large change in conformational entropy that opposes binding.
authors.affiliation: Department of Biotechnology, Royal Institute of Technology, S-10691 Stockholm, Sweden.
authors.forename: Vildan
authors.initials: V
authors.lastname: Dincbas-Renqvist
authors.forename: Christofer
authors.initials: C
authors.lastname: Lendel
authors.forename: Jakob
authors.initials: J
authors.lastname: Dogan
authors.forename: Elisabet
authors.initials: E
authors.lastname: Wahlberg
authors.forename: Torleif
authors.initials: T
authors.lastname: Härd
mesh_terms: D002352:Carrier Proteins / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D015202:Protein Engineering; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D002352:Carrier Proteins