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Published on: December 3, 2015
The pentapeptide GGAGG has PII conformation.
Liang Ding1, Kang Chen, Paul A Santini
1Department of Chemistry, New York University, 100 Washington Square East, New York, NY 10003, USA.
Journal of the American Chemical Society
|July 3, 2003
Summary
Unfolded proteins may adopt a significant population of PII structure, an extended left-handed helix. This study used model peptides to show alanine residues favor PII conformation, impacting unfolded protein entropy.
Area of Science:
- Protein structure and dynamics
- Biophysical chemistry
- Conformational analysis
Background:
- Protein structure is primarily studied in its native folded state.
- The structure of unfolded proteins, often termed "random coil," is less understood.
- Emerging evidence suggests unfolded proteins may adopt a prevalent PII helical structure.
Purpose of the Study:
- To investigate the conformational preferences of unfolded proteins using a model peptide system.
- To analyze the PII structure adoption by alanine residues in a minimal peptide.
- To explore the impact of temperature on protein secondary structure in an unfolded state.
Main Methods:
- Synthesis of AcGGXGGNH2 peptides, with X as alanine.
- Nuclear Magnetic Resonance (NMR) spectroscopy to determine dihedral angles (Phi and Psi).
- Circular Dichroism (CD) spectroscopy for secondary structure analysis.
- Temperature-dependent studies to observe conformational shifts.
Main Results:
- NMR data confirmed alanine's Phi and Psi angles (-73°, 125°) fall within the PII region of the Ramachandran plot.
- CD spectroscopy revealed a characteristic PII spectrum with strong negative absorbance at 190 nm.
- Temperature-dependent experiments indicated a shift towards beta-strand structures at elevated temperatures.
Conclusions:
- The model peptide AcGGAGGNH2 adopts a stable PII conformation, supporting its prevalence in unfolded proteins.
- Alanine residues, representing the peptide backbone, significantly contribute to the conformational entropy of unfolded polypeptides.
- These findings provide critical insights into the structural underpinnings of protein unfolding and conformational disorder.
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