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

Abstract

Searches in an EST database from maize revealed the expression of a protein related to the Galanthus nivalis (GNA) agglutinin, referred to as GNA maize. Heterologous expression of GNA maize in Pichia pastoris allowed characterization of the first nucleocytoplasmic GNA homolog from plants. GNA maize is a tetrameric protein which shares 64% sequence similarity with GNA. Glycan microarray analyses revealed important differences in the specificity. Unlike GNA, which binds strongly to high-mannose N-glycans, the lectin from maize reacts almost exclusively with more complex glycans. Interestingly, GNA maize prefers complex glycans containing β1-2 GlcNAc residues. The obvious difference in carbohydrate-binding properties is accompanied by a 100-fold reduced anti-HIV activity. Although the sequences of GNA and GNA maize are clearly related they show only 28% sequence identity. Our results indicate that gene divergence within the family of GNA-related lectins leads to changes in carbohydrate-binding specificity, as shown on N-glycan arrays.