title: Design of single-layer beta-sheets without a hydrophobic core.
abstract: The hydrophobic effect is the main thermodynamic driving force in the folding of water-soluble proteins. Exclusion of nonpolar moieties from aqueous solvent results in the formation of a hydrophobic core in a protein, which has been generally considered essential for specifying and stabilizing the folded structures of proteins. Outer surface protein A (OspA) from Borrelia burgdorferi contains a three-stranded beta-sheet segment which connects two globular domains. Although this single-layer beta-sheet segment is exposed to solvent on both faces and thus does not contain a hydrophobic core, the segment has a high conformational stability. Here we report the engineering of OspA variants that contain larger single-layer beta-sheets (comprising five and seven beta-strands) by duplicating a beta-hairpin unit within the beta-sheet. Nuclear magnetic resonance and small-angle X-ray scattering analyses reveal that these extended single-layer beta-sheets are formed as designed, and amide hydrogen-deuterium exchange and chemical denaturation show that they are stable. Thus, interactions within the beta-hairpin unit and those between adjacent units, which do not involve the formation of a hydrophobic core, are sufficient to specify and stabilize the single-layer beta-sheet structure. Our results provide an expanded view of protein folding, misfolding and design.
authors.affiliation: Department of Biochemistry and Biophysics, University of Rochester Medical Center, New York 14642, USA. Shohei_Koide@urmc.rochester.edu
authors.forename: S
authors.initials: S
authors.lastname: Koide
authors.forename: X
authors.initials: X
authors.lastname: Huang
authors.forename: K
authors.initials: K
authors.lastname: Link
authors.forename: A
authors.initials: A
authors.lastname: Koide
authors.forename: Z
authors.initials: Z
authors.lastname: Bu
authors.forename: D M
authors.initials: DM
authors.lastname: Engelman
mesh_terms: D000954:Antigens, Surface / Q000737:chemistry* / Q000235:genetics; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D001428:Bacterial Vaccines; D015748:Borrelia burgdorferi Group; D008074:Lipoproteins; D009682:Magnetic Resonance Spectroscopy; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012542:Scattering, Radiation
chemical_list: D000954:Antigens, Surface; D001425:Bacterial Outer Membrane Proteins; D001428:Bacterial Vaccines; D008074:Lipoproteins; C072045:OspA protein