Plant pathogens, like animal ones, use protein-carbohydrate interactions in their strategy for host recognition, attachment, and invasion. The bacterium Ralstonia solanacearum, which is distributed worldwide and causes lethal wilt in many agricultural crops, was shown to produce a potent L-fucose-binding lectin, R. solanacearum lectin, a small protein of 90 amino acids with a tandem repeat in its amino acid sequence. In the present study, surface plasmon resonance expts. conducted on a series of oligosaccharides show a preference for binding to aFuc1-2Gal and aFuc1-6Gal epitopes. Titrn. microcalorimetry demonstrates the presence of two binding sites per monomer and an unusually high affinity of the lectin for aFuc1-2Gal-contg. oligosaccharides (KD = 2.5 x 10-7 M for 2-fucosyllactose). R. solanacearum lectin has been crystd. with a Me deriv. of fucose and with the highest affinity ligand, 2-fucosyllactose. X-ray crystal structures, the one with a-methyl-fucoside being at ultrahigh resoln., reveal that each monomer consists of two small four-stranded anti-parallel b-sheets. Trimerization through a 3-fold or pseudo-3-fold axis generates a six-bladed b-propeller architecture, very similar to that previously described for the fungal lectin of Aleuria aurantia. This is the first report of a b-propeller formed by oligomerization and not by sequential domains. Each monomer presents two fucose binding sites, resulting in six sym. arranged sugar binding sites for the b-propeller. Crystals were also obtained for a mutated lectin complexed with a fragment of xyloglucan, a fucosylated polysaccharide from the primary cell wall of plants, which may be the biol. target of the lectin. [on SciFinder (R)]