title: Conformational switching in designed peptides: the helix/sheet transition.
abstract: BACKGROUND
  The structure adopted by peptides and proteins depends not only on the primary sequence, but also on conditions such as solvent polarity or method of sample preparation. We examined the effect that solution conditions have on the folded conformations of two peptides, one of which contains the photoisomerizable amino acid p-phenylazo-L-phenylalanine.
  
  
  RESULTS
  Spectroscopic studies indicate that these two peptides switch between helical and beta sheet conformations. The switch behavior is influenced by solution conditions including pH, NaCl concentration, temperature, and peptide concentration. The CD spectrum of the peptide containing p-phenylazo-L-phenylalanine changes from a spectrum characteristic of a beta sheet to one characteristic of an alpha helix upon irradiation.
  
  
  CONCLUSIONS
  We hypothesize that the structural states of the peptides are a monomeric alpha helix and an aggregated antiparallel beta sheet. Conditions encouraging aggregation tend to favor sheet; conditions discouraging aggregation tend to favor helix. Consideration of such solution-dependent conformational changes may affect de novo protein design and have a bearing on certain biological processes.
authors.affiliation: Graduate Group in Biophysics, University of California, San Francisco 94143, USA.
authors.forename: R
authors.initials: R
authors.lastname: Cerpa
authors.forename: F E
authors.initials: FE
authors.lastname: Cohen
authors.forename: I D
authors.initials: ID
authors.lastname: Kuntz
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D015195:Drug Design; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D010777:Photochemistry; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012965:Sodium Chloride; D012996:Solutions; D013696:Temperature
chemical_list: D010455:Peptides; D012996:Solutions; D012965:Sodium Chloride