title: Mutational analysis of designed peptides that undergo structural transition from alpha helix to beta sheet and amyloid fibril formation.
abstract: BACKGROUND
  Conformational alteration and fibril formation of proteins have a key role in a variety of amyloid diseases. A simplified model peptide would lead to a better understanding of underlying mechanisms whereby protein misfolding and aggregation occur. Recently, we reported the design of peptides that undergo a self-initiated structural transition from an alpha helix to a beta sheet and form amyloid fibrils. In this study, we focus on two glutamine residues in the peptide, and report a mutational analysis of these residues.
  
  
  RESULTS
  A coiled-coil alpha-helix structure bearing a hydrophobic adamantanecarbonyl (Ad) group at the N terminus was designed (parent peptide Ad-QQ). In neutral aqueous solution, the double Gln-->Ala mutant (Ad-AA) underwent the alpha-->beta structural transition within four hours, which was similar to the case of Ad-QQ. In contrast, two kinds of single Gln-->Ala mutant (Ad-QA and Ad-AQ) required three days for the transition. Furthermore, Ad-QQ and Ad-AA formed amyloid fibrils, whereas Ad-QA and Ad-AQ did not. Interestingly, however, Ad-QA and Ad-AQ complementarily assembled into the fibrils when they were mixed.
  
  
  CONCLUSIONS
  The Gln-->Ala substitution in the peptide significantly alters the alpha-->beta transitional properties and the ability to form amyloid fibrils. A heterogeneous assembly of two peptide species into the fibrils is also presented. These results suggest that the secondary structural transition and self-assembly into the well-organized fibril may depend strictly on the primary structure, which determines the beta-sheet packing. The results might provide insights into misfolding and fibril formation of disease-associated mutant proteins.
authors.affiliation: Department of Bioengineering, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 226-8501, Yokohama, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Takahashi
authors.forename: A
authors.initials: A
authors.lastname: Ueno
authors.forename: H
authors.initials: H
authors.lastname: Mihara
mesh_terms: D000595:Amino Acid Sequence; D000682:Amyloid / Q000737:chemistry*; D002942:Circular Dichroism; D007700:Kinetics; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D013329:Structure-Activity Relationship
chemical_list: D000682:Amyloid; D010455:Peptides