%A SA Asher
%A AV Mikhonin
%A S Bykov
%J Journal of the American Chemical Society
%T UV Raman demonstrates that ?-helical polyalanine peptides melt to polyproline II conformations
%X 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 (Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 9190). The UV Raman spectra of XAO are essentially identical to the spectra of small peptides such as ala5 and to the large 21 -residue predominantly Ala peptide, AP. We conclude that the non-?-helical conformations of these peptides are dominantly PPII. Thus, AP, which is highly ?-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 ?-angle to the amide III band frequency. We describe a new method to estimate the Ramachandran ?-angular distributions from amide III band line shapes measured in 204-nm UV Raman spectra. We used this method to compare the ?-distributions in XAO, ala5, the non-?-helical state of AP, and acid-denatured apomyoglobin. In addition, we estimated the ?-angle distributions of peptide bonds which occur in non-?-helix and non-?-sheet conformations in a small library of proteins.
%N 27
%P 8433 - 8440
%V 126
%D 2004
%R 10.1021/ja049518j
%L pittir17176