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A Novel Technique for Raman Analysis of Highly Radioactive Samples Using Any Standard Micro-Raman Spectrometer
Published on: April 12, 2017
UV Raman demonstrates that alpha-helical polyalanine peptides melt to polyproline II conformations
Sanford A Asher1, Alexander V Mikhonin, Sergei Bykov
1Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA. asher@pitt.edu
Journal of the American Chemical Society
|July 9, 2004
Summary
Peptides in solution adopt a dominant polyproline II (PPII) conformation, not disordered states. UV Raman spectroscopy provides a new method to analyze peptide structures and Ramachandran Psi-angle distributions.
Area of Science:
- Biophysics
- Spectroscopy
- Structural Biology
Background:
- Nuclear Magnetic Resonance (NMR) studies indicated peptide XAO adopts a polyproline II (PPII) conformation in aqueous solution.
- Small peptides like ala(5) and a larger alanine-rich peptide (AP) share similar spectral features with XAO.
Purpose of the Study:
- To investigate the secondary structures of peptides in solution using UV Raman spectroscopy.
- To develop and apply a novel method for estimating Ramachandran Psi-angle distributions from amide III band frequencies.
- To compare Psi-angle distributions across various peptides and proteins.
Main Methods:
- 204-nm UV Raman spectroscopy was employed to analyze peptide conformations.
- A new method was developed to correlate amide III band frequencies with Ramachandran Psi-angles.
- Psi-angular distributions were estimated for XAO, ala(5), the non-alpha-helical state of AP, acid-denatured apomyoglobin, and peptide bonds in proteins.
Main Results:
- UV Raman spectra of XAO, ala(5), and AP were nearly identical, suggesting a dominant PPII conformation for non-alpha-helical states.
- The peptide AP transitions from an alpha-helical state to a PPII conformation.
- No evidence for intermediate disordered conformations was observed.
- The developed method successfully estimated Psi-angular distributions for various peptide and protein samples.
Conclusions:
- Non-alpha-helical conformations in these peptides are predominantly PPII.
- UV Raman spectroscopy is a valuable tool for structural analysis of peptides and proteins.
- The new method provides insights into the Ramachandran Psi-angle distributions in diverse structural contexts.
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