title: Analysis of the factors that stabilize a designed two-stranded antiparallel beta-sheet.
abstract: Autonomously folding beta-hairpins (two-strand antiparallel beta-sheets) have become increasingly valuable tools for probing the forces that control peptide and protein conformational preferences. We examine the effects of variations in sequence and solvent on the stability of a previously designed 12-residue peptide (1). This peptide adopts a beta-hairpin conformation containing a two-residue loop (D-Pro-Gly) and a four-residue interstrand sidechain cluster that is observed in the natural protein GB1. We show that the conformational propensity of the loop segment plays an important role in beta-hairpin stability by comparing 1 with (D)P--> N mutant 2. In addition, we show that the sidechain cluster contributes both to conformational stability and to folding cooperativity by comparing 1 with mutant 3, in which two of the four cluster residues have been changed to serine. Thermodynamic analysis suggests that the high loop-forming propensity of the (D)PG segment decreases the entropic cost of beta-hairpin formation relative to the more flexible NG segment, but that the conformational rigidity of (D)PG may prevent optimal contacts between the sidechains of the GB1-derived cluster. The enthalpic favorability of folding in these designed beta-hairpins suggests that they are excellent scaffolds for studying the fundamental mechanisms by which amino acid sidechains interact with one another in folded proteins.
authors.affiliation: Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: Juan F
authors.initials: JF
authors.lastname: Espinosa
authors.forename: Faisal A
authors.initials: FA
authors.lastname: Syud
authors.forename: Samuel H
authors.initials: SH
authors.lastname: Gellman
mesh_terms: D000595:Amino Acid Sequence; D004355:Drug Stability; D006801:Humans; D009154:Mutation; D019906:Nuclear Magnetic Resonance, Biomolecular; D009842:Oligopeptides / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary / Q000187:drug effects / Q000235:genetics; D018080:Receptors, GABA-B / Q000737:chemistry*; D012997:Solvents / Q000494:pharmacology; D013816:Thermodynamics
chemical_list: D009842:Oligopeptides; D018080:Receptors, GABA-B; D012997:Solvents