A cyclic beta-strand tripeptide with an alpha-helix like CD spectrum
Russell W Driver1, Huy N Hoang, Giovanni Abbenante
1Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld 4072, Australia.
Organic Letters
|June 19, 2009
Summary
Circular dichroism (CD) spectra can misrepresent peptide structures. A cyclic peptide, cyclo-(1,3)-[ALE]-NH(2), showed an alpha-helix CD spectrum but NMR revealed antiparallel beta-strands, demonstrating CD
Area of Science:
- Biochemistry
- Structural Biology
- Peptide Chemistry
Background:
- Protein secondary structures like alpha-helices are typically characterized by 3.6 amino acids per turn.
- Circular dichroism (CD) spectroscopy is a common technique for analyzing protein secondary structures.
Purpose of the Study:
- To investigate the structural characteristics of a cyclized tripeptide, cyclo-(1,3)-[ALE]-NH(2).
- To evaluate the reliability of CD spectroscopy in determining peptide secondary structures.
Main Methods:
- Synthesis of the cyclic peptide cyclo-(1,3)-[ALE]-NH(2) via side chain to N-terminus lactam bond.
- Analysis of secondary structure using circular dichroism (CD) spectroscopy.
- Determination of detailed molecular structure using proton nuclear magnetic resonance (NMR) spectroscopy.
Main Results:
- Cyclo-(1,3)-[ALE]-NH(2) exhibited a CD spectrum characteristic of an alpha-helix.
- Proton NMR spectra revealed a novel cyclic peptide structure comprising two antiparallel beta-strands.
- These beta-strands were connected by an alanine-leucine cis-amide bond, with no observed hydrogen bonding.
Conclusions:
- The study demonstrates that CD spectra alone can be misleading in characterizing peptide secondary structures.
- Proton NMR provided a more accurate structural elucidation, revealing a beta-strand conformation.
- This highlights the importance of employing multiple spectroscopic techniques for definitive structural assignment.
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