Designed beta-hairpin peptides with defined tight turn stereochemistry

Area of Science:

• Biochemistry
• Structural Biology
• Peptide Chemistry

Background:

• Beta-hairpin structures are crucial motifs in protein folding.
• Understanding the role of beta-turns is key to designing stable peptide structures.
• Stereochemistry at beta-turns can significantly impact peptide conformation.

Purpose of the Study:

• To investigate the effect of beta-turn stereochemistry on designed beta-hairpin conformations.
• To compare the conformational preferences of two synthetic octapeptides with differing D-Pro-beta-amino acid linkages.
• To elucidate the structural basis for beta-hairpin formation and stability.

Main Methods:

• Conformational analysis using 500 MHz proton nuclear magnetic resonance ((1)H NMR) spectroscopy.
• Nuclear Overhauser effect (NOE) studies to determine specific interactions and conformations.
• X-ray crystallography to obtain high-resolution structural data.
• Circular dichroism (CD) spectroscopy to analyze secondary structure content.

Main Results:

• Both synthetic octapeptides predominantly adopt beta-hairpin conformations in methanol solution.
• Peptide 1 exhibits a type II' beta-turn (D-Pro-L-Ala), while peptide 2 shows a type I' beta-turn (D-Pro-D-Ala).
• X-ray crystallography of peptide 1 confirms a beta-hairpin structure nucleated by a type II' beta-turn and stabilized by three hydrogen bonds.
• Distinct CD spectra for peptides 1 and 2 suggest differences in their conformational ensembles.

Conclusions:

• Beta-turn stereochemistry critically dictates the conformational outcome of designed beta-hairpin structures.
• The D-Pro-L-Ala sequence favors a type II' beta-turn, leading to stable beta-hairpin formation.
• The D-Pro-D-Ala sequence predominantly forms a type I' beta-turn, potentially influencing the overall structure and dynamics.