title: Cyclic modular beta-sheets.
abstract: The development of peptide beta-hairpins is problematic, because folding depends on the amino acid sequence and changes to the sequence can significantly decrease folding. Robust beta-hairpins that can tolerate such changes are attractive tools for studying interactions involving protein beta-sheets and developing inhibitors of these interactions. This paper introduces a new class of peptide models of protein beta-sheets that addresses the problem of separating folding from the sequence. These model beta-sheets are macrocyclic peptides that fold in water to present a pentapeptide beta-strand along one edge; the other edge contains the tripeptide beta-strand mimic Hao [JACS 2000, 122, 7654] and two additional amino acids. The pentapeptide and Hao-containing peptide strands are connected by two delta-linked ornithine (deltaOrn) turns [JACS 2003, 125, 876]. Each deltaOrn turn contains a free alpha-amino group that permits the linking of individual modules to form divalent beta-sheets. These "cyclic modular beta-sheets" are synthesized by standard solid-phase peptide synthesis of a linear precursor followed by solution-phase cyclization. Eight cyclic modular beta-sheets 1a-1h containing sequences based on beta-amyloid and macrophage inflammatory protein 2 were synthesized and characterized by 1H NMR. Linked cyclic modular beta-sheet 2, which contains two modules of 1b, was also synthesized and characterized. 1H NMR studies show downfield alpha-proton chemical shifts, deltaOrn delta-proton magnetic anisotropy, and NOE cross-peaks that establish all compounds but 1c and 1g to be moderately or well folded into a conformation that resembles a beta-sheet. Pulsed-field gradient NMR diffusion experiments show little or no self-association at low (</=2 mM) concentrations. Changes to the residues in the Hao-containing strands of 1c and 1g improve folding and show that folding of the structures can be enhanced without altering the sequence of the pentapeptide strand. Well-folded cyclic modular beta-sheets 1a, 1b, and 1f each have a phenylalanine directly across from Hao, suggesting that cyclic modular beta-sheets containing aromatic residues across from Hao are better folded.
authors.affiliation: Department of Chemistry, University of California-Irvine, Irvine, CA 92697-2025, USA.
authors.forename: R Jeremy
authors.initials: RJ
authors.lastname: Woods
authors.forename: Justin O
authors.initials: JO
authors.lastname: Brower
authors.forename: Elena
authors.initials: E
authors.lastname: Castellanos
authors.forename: Mehrnoosh
authors.initials: M
authors.lastname: Hashemzadeh
authors.forename: Omid
authors.initials: O
authors.lastname: Khakshoor
authors.forename: Wade A
authors.initials: WA
authors.lastname: Russu
authors.forename: James S
authors.initials: JS
authors.lastname: Nowick
mesh_terms: D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry; D054426:Chemokine CXCL2; D002851:Chromatography, High Pressure Liquid; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D015846:Monokines / Q000737:chemistry; D009842:Oligopeptides / Q000138:chemical synthesis*; D009952:Ornithine / Q000737:chemistry; D010456:Peptides, Cyclic / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D014867:Water / Q000737:chemistry
chemical_list: D016229:Amyloid beta-Peptides; D054426:Chemokine CXCL2; D015846:Monokines; D009842:Oligopeptides; D010456:Peptides, Cyclic; D014867:Water; D009952:Ornithine