A Novel Fucose-binding Lectin from Photorhabdus luminescens (PLL) with an Unusual Heptabladed β-Propeller Tetrameric Structure

Abstract

Photorhabdus luminescens is known for its symbiosis with the entomopathogenic nematode Heterorhabditis bacteriophora and its pathogenicity toward insect larvae. A hypothetical 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-Glcβ1-4(2,3-O-Me)Rhaα-O-(p-CH)-OCHCHNH PLL was discovered to be a homotetramer with an intersubunit disulfide bridge. The crystal structures of native and recombinant PLL revealed a seven-bladed β-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.

Lectin PLL3, a Novel Monomeric Member of the Seven-Bladed β-Propeller Lectin Family

“…Structural studies of lectins from opportunistic fungal and bacterial pathogens show that these lectins interact with carbohydrates on the surface of host cells and they mediate adhesion, which can lead to initiating infection [12][13][14]. It is expected that lectins may play an important role in the life cycle of the Photorhabdus-Heterorhabditis complex [15][16][17]. They can mediate mutualism interactions, be involved in pathogenicity toward insect larva, or facilitate intermediate communication within the bacterial population.Recently, a family of structurally related lectins was discovered in the bacterial genus Photorhabdus [15][16][17].…”

“…It is expected that lectins may play an important role in the life cycle of the Photorhabdus-Heterorhabditis complex [15][16][17]. They can mediate mutualism interactions, be involved in pathogenicity toward insect larva, or facilitate intermediate communication within the bacterial population.Recently, a family of structurally related lectins was discovered in the bacterial genus Photorhabdus [15][16][17]. These lectins share a seven-bladed β-propeller fold with multiple binding sites located between the blades.…”

“…laumondii), occurs as a tetramer, whereas PLL2 from the same species and PHL from P. asymbiotica subsp. asymbiotica are dimers [15][16][17]. Studies show that these carbohydrate-binding proteins can interact with insect and human immune systems.…”

“…Studies show that these carbohydrate-binding proteins can interact with insect and human immune systems. For instance, PHL binds to hemocytes [15], and PLL interacts with the nematode cuticle [16]. Moreover, PHL and PLL2 participate in the immunosuppression by the inhibition of a production of the reactive oxygen species [15,17].…”

“…These lectins exhibit affinity toward l-fucose and its derivatives; PHL can recognize also other saccharides such as d-glucose or d-galactose. Interestingly, they were both shown to interact with O-methylated saccharides [15,16]. O-methylated glycans are often present in some species of bacteria, fungi, algae, plants, and worms such as nematodes, but not in mammals nor insects [18].…”