title: Self-Assembly of a Designed Alternating Arginine/Phenylalanine Oligopeptide.
abstract: A model octapeptide peptide consisting of an alternating sequence of arginine (Arg) and phenylalanine (Phe) residues, namely, [Arg-Phe]4, was prepared, and its self-assembly in solution studied. The simple alternating [Arg-Phe]4 peptide sequence allows for unique insights into the aggregation process and the structure of the self-assembled motifs. Fluorescence and UV-vis assays were used to determine critical aggregation concentrations, corresponding to the formation of oligomeric species and β-sheet rich structures organized into both spheroidal aggregates and highly ordered fibrils. Electron and atomic force microscopy images show globular aggregates and long unbranched fibers with diameters ranging from ∼4 nm up to ∼40 nm. Infrared and circular dichroism spectroscopy show the formation of β-sheet structures. X-ray diffraction on oriented stalks show that the peptide fibers have an internal lamellar structure, with an orthorhombic unit cell with parameters a ∼ 27.6 Å, b ∼ 9.7 Å, and c ∼ 9.6 Å. In situ small-angle X-ray scattering (SAXS) shows the presence of low molecular weight oligomers in equilibrium with mature fibers which are likely made up from 5 or 6 intertwined protofilaments. Finally, weak gel solutions are probed under gentle shear, suggesting the ability of these arginine-rich fibers to form networks.
authors.affiliation: †Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André 09210-580, Brazil.
authors.forename: Carla C
authors.initials: CC
authors.lastname: Decandio
authors.affiliation: †Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André 09210-580, Brazil.|‡Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, United Kingdom.
authors.forename: Emerson R
authors.initials: ER
authors.lastname: Silva
authors.affiliation: ‡Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, United Kingdom.
authors.forename: Ian W
authors.initials: IW
authors.lastname: Hamley
authors.affiliation: ‡Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, United Kingdom.
authors.forename: Valeria
authors.initials: V
authors.lastname: Castelletto
authors.affiliation: †Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André 09210-580, Brazil.
authors.forename: Michelle S
authors.initials: MS
authors.lastname: Liberato
authors.affiliation: †Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André 09210-580, Brazil.
authors.forename: Vani X
authors.initials: VX
authors.lastname: Oliveira
authors.affiliation: §Instituto de Física, Universidade de São Paulo, São Paulo 05314970, Brazil.
authors.forename: Cristiano L P
authors.initials: CL
authors.lastname: Oliveira
authors.affiliation: †Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André 09210-580, Brazil.
authors.forename: Wendel A
authors.initials: WA
authors.lastname: Alves
mesh_terms: D001120:Arginine / Q000737:chemistry*; D005782:Gels; D018625:Microscopy, Atomic Force; D046529:Microscopy, Electron, Transmission; D009842:Oligopeptides / Q000737:chemistry*; D010649:Phenylalanine / Q000737:chemistry*; D066329:Protein Aggregates; D017433:Protein Structure, Secondary; D012996:Solutions
chemical_list: D005782:Gels; D009842:Oligopeptides; D066329:Protein Aggregates; D012996:Solutions; D010649:Phenylalanine; D001120:Arginine