UV Raman studies of peptide conformation demonstrate that betanova does not cooperatively unfold.
We used UV resonance Raman spectroscopy (UVRR) excited within the peptide bond pi --> pi* electronic transitions and within the aromatic amino acid pi --> pi* electronic transitions to examine the temperature dependence of the solution conformation of betanova, a 20-residue beta-sheet polypeptide [Kortemme, T., Ramirez-Alvarado, M., and Serrano, L. (1998) Science 281, 253-256]. The 206.5 nm excited UVRR enhances the amide vibrations and demonstrates that betanova has a predominantly beta-sheet structure between 5 and 82 degrees C. The 229 nm excited UVRR, which probes the tyrosine and tryptophan side chain vibrations, shows an increase in the solvent exposure of the tryptophan side chains as the temperature is increased. Our results are consistent with the existence of an intermediate state similar to that calculated by Bursulaya and Brooks [Bursulaya, B. D., and Brooks, C. L. (1999) J. Am. Chem. Soc. 121, 9947-9951] and exclude the previously proposed two-state cooperative folding mechanism. Betanova's structure appears to be molten globule over the 3-82 degrees C temperature range of our study.
Boyden
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MN
Department of Chemistry, Chevron Science Center, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
Asher
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SA
D002942:Circular Dichroism; D010455:Peptides / Q000737:chemistry; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman / Q000379:methods*
D010455:Peptides; D011506:Proteins; C113273:betanova protein, synthetic