Photorhabdus luminescens is known for its symbiosis with the entomopathogenic nematode Heterorhabditis bacteriophora and its pathogenicity toward insect larvae. Ahypothetical protein from P. luminescens was identified, purified from the native source, and characterized as an L-fucose-binding lectin, named P. luminescens lectin (PLL). Glycan array and biochemical characterization data revealed PLL to be specific toward L-fucose and the disaccharide glycan 3,6-O-Me-2-Glc beta 1-4(2,3-O-Me-2)Rha alpha-O-(p-C6H4)-OCH2CH2NH2. PLL was discovered to be a homotetramer with an intersubunit disulfide bridge. The crystal structures of native and recombinant PLL revealed a seven-bladed beta-propeller fold creating seven putative fucose-binding sites per monomer. The crystal structure of the recombinant PLL.L-fucose complex confirmed that at least three sites were fucose-binding. Moreover, the crystal structures indicated that some of the other sites are masked either by the tetrameric nature of the lectin or by incorporation of the C terminus of the lectin into one of these sites. PLL exhibited an ability to bind to insect hemocytes and the cuticular surface of a nematode, H. bacteriophora.