title: Anion effect on the nanostructure of a metal ion binding self-assembling peptide.
abstract: Effects of copper salts containing different anions (SO(4)(2)(-), Cl(-), and NO(3)(-)) on the self-assembly of a designed peptide EAK16(II)GGH with affinity for Cu(2+) have been investigated. The peptide secondary structure, self-assembled nanostructures, and surface activity were observed to depend strongly on the type of anion. Over a salt concentration range from 0.05 to 10.0 mM, SO(4)(2)(-) induced long fiber formation, whereas Cl(-) and NO(3)(-) caused short fiber formation. The fiber length increased with copper sulfate concentration, but the concentration of copper chloride and copper nitrate did not affect the peptide nanostructures significantly. Analysis by Fourier transform infrared spectroscopy (FTIR) revealed that the addition of the copper salts tended to cause the peptide conformation to change from alpha-helix/random coil to beta-sheet, the extent to which depended on the anion type. This evidence of the anion effect was also supported by surface tension measurements using the axisymmetric drop shape analysis-profile (ADSA-P) technique. An explanation for the effect of anions on the peptide self-assembly was proposed. The divalent anion SO(4)(2)(-) might serve as a bridge by electrostatically interacting with two lysine residues from different peptide molecules, promoting beta-sheet formation. The extensive beta-sheet formation may further promote peptide self-assembly into long fibers. On the other hand, monovalent anions Cl(-) and NO(3)(-) may only electrostatically interact with one charged residue of the peptide; hence, a mixed secondary structure of alpha-helix/random coil and beta-sheet was observed. This observation might explain the predominant formation of short fibers in copper chloride and copper nitrate solutions.
authors.affiliation: Department of Chemical Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: H
authors.initials: H
authors.lastname: Yang
authors.forename: M
authors.initials: M
authors.lastname: Pritzker
authors.forename: S Y
authors.initials: SY
authors.lastname: Fung
authors.forename: Y
authors.initials: Y
authors.lastname: Sheng
authors.forename: W
authors.initials: W
authors.lastname: Wang
authors.forename: P
authors.initials: P
authors.lastname: Chen
mesh_terms: D000838:Anions / Q000737:chemistry; D002413:Cations, Divalent / Q000737:chemistry; D003300:Copper / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D010455:Peptides / Q000737:chemistry*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D055672:Static Electricity
chemical_list: D000838:Anions; D002413:Cations, Divalent; D010455:Peptides; D003300:Copper