title: UV Raman demonstrates that alpha-helical polyalanine peptides melt to polyproline II conformations.
abstract: We examined the 204-nm UV Raman spectra of the peptide XAO, which was previously found by Shi et al.'s NMR study to occur in aqueous solution in a polyproline II (PPII) conformation. The UV Raman spectra of XAO are essentially identical to the spectra of small peptides such as ala(5) and to the large 21-residue predominantly Ala peptide, AP. We conclude that the non-alpha-helical conformations of these peptides are dominantly PPII. Thus, AP, which is highly alpha-helical at room temperature, melts to a PPII conformation. There is no indication of any population of intermediate disordered conformations. We continued our development of methods to relate the Ramachandran Psi-angle to the amide III band frequency. We describe a new method to estimate the Ramachandran Psi-angular distributions from amide III band line shapes measured in 204-nm UV Raman spectra. We used this method to compare the Psi-distributions in XAO, ala(5), the non-alpha-helical state of AP, and acid-denatured apomyoglobin. In addition, we estimated the Psi-angle distributions of peptide bonds which occur in non-alpha-helix and non-beta-sheet conformations in a small library of proteins.
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA. asher@pitt.edu
authors.forename: Sanford A
authors.initials: SA
authors.lastname: Asher
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Mikhonin
authors.forename: Sergei
authors.initials: S
authors.lastname: Bykov
mesh_terms: D000577:Amides / Q000737:chemistry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013696:Temperature
chemical_list: D000577:Amides; D010455:Peptides; C011083:polyproline; C019529:polyalanine