Related lectins from snowdrop and maize differ in their carbohydrate-binding specificity

Area of Science:

• Plant biochemistry
• Molecular biology
• Glycobiology

Background:

• Galanthus nivalis agglutinin (GNA) is a well-characterized plant lectin known for its high-mannose N-glycan binding.
• Plant lectins play diverse roles, including defense and signaling, often mediated by carbohydrate-binding specificities.

Purpose of the Study:

• To identify and characterize a novel GNA homolog from maize.
• To investigate the carbohydrate-binding specificity and functional properties of the maize GNA homolog.
• To understand the evolutionary implications of gene divergence on lectin function.

Main Methods:

• Expressed sequence tag (EST) database mining in maize to identify GNA-related sequences.
• Heterologous expression of the maize GNA homolog (GNA(maize)) in Pichia pastoris.
• Biochemical characterization including tetramer formation and glycan microarray analysis.
• Comparison of sequence identity and carbohydrate-binding properties with GNA.

Main Results:

• Identification and successful expression of GNA(maize), the first nucleocytoplasmic GNA homolog from plants.
• GNA(maize) is a tetrameric protein with 64% sequence similarity but only 28% sequence identity to GNA.
• Unlike GNA's preference for high-mannose glycans, GNA(maize) binds complex glycans, particularly those with beta1-2 GlcNAc residues.
• GNA(maize) exhibits a 100-fold reduction in anti-HIV activity compared to GNA.

Conclusions:

• Gene divergence within GNA-related lectin families leads to significant alterations in carbohydrate-binding specificity.
• The distinct glycan-binding profile of GNA(maize) suggests specialized roles in maize compared to GNA.
• These findings provide insights into the evolution of lectin function and specificity in plants.