Several thaumatin-like proteins bind to beta-1,3-glucans

Area of Science:

• Plant Biochemistry
• Molecular Biology
• Protein-Polysaccharide Interactions

Background:

• Plant stress responses involve pathogenesis-related (PR) proteins.
• PR proteins play roles in plant defense mechanisms.
• Understanding PR protein interactions with cell wall components is crucial.

Purpose of the Study:

• To investigate the binding specificities of PR proteins from stressed barley leaves.
• To identify the polysaccharides that interact with these barley PR proteins.
• To characterize the nature and properties of these protein-polysaccharide interactions.

Main Methods:

• Analysis of intercellular fluid washings from stressed barley leaves.
• Binding assays using water-insoluble polysaccharides, specifically beta-1,3-glucans like pachyman.
• Protein release and re-binding experiments under various conditions (pH, temperature, denaturants).
• N-terminal sequencing and homology analysis of identified proteins.

Main Results:

• Three barley PR proteins (19, 16, and 15 kD) specifically bound to water-insoluble beta-1,3-glucans.
• Binding to pachyman was efficient under various conditions and stable.
• Bound proteins could be released by acid or SDS-boiling and subsequently re-bind.
• N-terminal sequences revealed homology to thaumatin-like (TL) proteins, including known antifungal proteins.
• Extracellular pea proteins homologous to TL proteins also bound to pachyman.

Conclusions:

• Barley PR proteins exhibit specific binding to beta-1,3-glucans, suggesting a role in cell wall interactions.
• These interactions are robust and reversible, indicating functional significance.
• The identified proteins belong to the thaumatin-like protein family, known for antifungal activity.
• This binding capability might be a mechanism for deploying antifungal defenses in plants.