gamma-Zein secondary structure in solution by circular dichroism

Area of Science:

• Plant protein structure
• Biophysical characterization
• Maize storage proteins

Background:

• The N-terminal domain of gamma-zein, rich in proline, plays a role in cell membrane crossing.
• A synthetic hexapeptide (PPPVHL) from gamma-zein's N-terminus can adopt a polyproline II (PPII) conformation in solution.
• Previous studies using solid-state spectroscopies could not quantify PPII content in gamma-zein due to signal overlap.

Purpose of the Study:

• To analyze the secondary structure of gamma-zein, focusing on PPII conformation.
• To overcome limitations of solid-state techniques for PPII measurement in physiological environments.
• To determine PPII content in gamma-zein under various solution conditions.

Main Methods:

• Circular dichroism spectroscopy was employed to analyze gamma-zein's secondary structure.
• Experiments were conducted in SDS aqueous solution (with and without DTT) and in 60% 2-propanol/water with DTT.
• Spectroscopic data were analyzed to differentiate and quantify secondary structure elements.

Main Results:

• Gamma-zein exhibited high helical content across all tested solutions.
• The polyproline II (PPII) conformation was detected at approximately 7% specifically in the water/DTT solution.
• SDS and 2-propanol solutions did not significantly promote the PPII conformation.

Conclusions:

• Gamma-zein maintains a predominantly helical structure in various aqueous and solvent conditions.
• The PPII conformation in gamma-zein is context-dependent and can be observed under specific reducing conditions.
• Circular dichroism provides a viable method for assessing PPII content in gamma-zein, overcoming previous limitations.