title: Long-range interactions stabilize the fold of a non-natural oligomer.
abstract: Toward designing nonbiological polymers that fold into predictable tertiary structures, we report a "beta-oligomer" composed of beta-amino acids that adopts a cooperatively folded structure. We have computationally designed a C(2)-symmetrical pair of interacting 14-helical beta-oligomers stabilized via long-range interhelical interactions and stapled together by a disulfide bond. The reduced (BHBred) and oxidized (BHBox) forms of the synthetic beta-oligomer represent the individual isolated helices and the two-helix bundle, respectively. We also prepared a third monomeric synthetic beta-oligomer (BHBmon) to avoid inadvertent disulfide formation during characterization. Circular dichroism spectroscopy revealed that BHBox showed a 2-fold increase in secondary structure, relative to the monohelical controls, BHBred and BHBmon. Further, BHBox showed a sigmoidal thermal unfolding curve with a per-residue van't Hoff enthalpy of approximately 0.7 kcal/(mol.residue), analogous to folded proteins. In contrast, BHBmon shows a broad thermal transition, typical of multistate unfolding for monomeric helices. Also, analytical ultracentrifugation showed that BHBmon and BHBox were monomeric at concentrations < or =800 and 280 microM, respectively. Therefore, the enhanced helicity of BHBox could be attributed to intramolecular helix-helix interactions.
authors.affiliation: Johnson Research Foundation, Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6059, USA.
authors.forename: Richard P
authors.initials: RP
authors.lastname: Cheng
authors.forename: William F
authors.initials: WF
authors.lastname: DeGrado
mesh_terms: D000613:Aminobutyrates / Q000737:chemistry; D002208:Caproates / Q000737:chemistry; D002942:Circular Dichroism; D009842:Oligopeptides / Q000737:chemistry*; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D014631:Valerates / Q000737:chemistry
chemical_list: D000613:Aminobutyrates; D002208:Caproates; D009842:Oligopeptides; D014631:Valerates; C047667:3-aminobutyric acid