title: Thermodynamic origin of α-helix stabilization by side-chain cross-links in a small protein.
abstract: Peptide cross-linking has been widely explored as a means of constraining short sequences into stable folded conformations, most commonly α-helices. The prevailing hypothesis for the origin of helix stabilization is an entropic effect resulting from backbone pre-organization; however, obtaining direct evidence bearing on this hypothesis is challenging. Here, we compare the folding thermodynamics of a small helix-rich protein domain and analogues containing one of three common cross-linking motifs. Analysis of the folding free energy landscapes of linear vs. cyclized species reveal consistent trends in the effect of cyclization on folding energetics, as well as subtle differences based on the chemistry of the cross link. Stabilization in all three systems arises entirely from a reduction in the entropic penalty of folding that more than compensates for an enthalpic destabilization of the folded state.
authors.affiliation: Department of Chemistry, University of Pittsburgh, 219 Parkman Ave., Pittsburgh, PA 15260, USA. horne@pitt.edu.
authors.forename: Conor M
authors.initials: CM
authors.lastname: Haney
authors.affiliation: Department of Chemistry, University of Pittsburgh, 219 Parkman Ave., Pittsburgh, PA 15260, USA. horne@pitt.edu.
authors.forename: Halina M
authors.initials: HM
authors.lastname: Werner
authors.affiliation: Department of Chemistry, University of Pittsburgh, 219 Parkman Ave., Pittsburgh, PA 15260, USA. horne@pitt.edu.
authors.forename: James J
authors.initials: JJ
authors.lastname: McKay
authors.affiliation: Department of Chemistry, University of Pittsburgh, 219 Parkman Ave., Pittsburgh, PA 15260, USA. horne@pitt.edu.
authors.forename: W Seth
authors.initials: WS
authors.lastname: Horne
mesh_terms: D008958:Models, Molecular; D055550:Protein Stability; D017433:Protein Structure, Secondary; D011506:Proteins / Q000138:chemical synthesis / Q000737:chemistry* / Q000302:isolation & purification; D013816:Thermodynamics
chemical_list: D011506:Proteins