Selected wheat seed defense proteins exhibit competitive binding to model microbial lipid interfaces

Area of Science:

• Biochemistry
• Plant Science
• Molecular Biology

Background:

• Puroindolines (Pins) and purothionins (Pths) are cysteine-rich proteins in wheat.
• These proteins contribute to plant defense against microbial pathogens.
• Their interaction with lipid layers is crucial for understanding their function.

Purpose of the Study:

• To investigate the co-adsorption and sequential binding of Pins and beta-purothionin (β-Pth) to model anionic lipid layers.
• To elucidate the distinct binding mechanisms of different Pins (Pin-a, Pin-b, mutant Pin-b) and β-Pth.
• To understand the role of hydrophobic and cationic residues in protein-lipid interactions and antimicrobial activity.

Main Methods:

• Surface pressure measurements
• External reflection Fourier-transform infrared (FTIR) spectroscopy
• Neutron reflectometry

Main Results:

• Pin-a formed a layer inhibiting β-Pth penetration.
• Wild-type Pin-b exhibited co-operative binding with β-Pth.
• Mutant Pin-b failed to bind the lipid layer in the presence of β-Pth.
• Differences in protein binding mechanisms and competitive interactions were observed.

Conclusions:

• Protein-lipid interactions are specific and influenced by protein structure.
• Hydrophobic and cationic residues play a key role in the antimicrobial function of Pins and Pths.
• Understanding these interactions provides insight into plant defense mechanisms.