title: A novel β-trefoil lectin from the parasol mushroom (Macrolepiota procera) is nematotoxic.
abstract: Lectins are carbohydrate-binding proteins present in all organisms. Some cytoplasmic lectins from fruiting bodies of dikaryotic fungi are toxic against a variety of parasites and predators. We have isolated, cloned and expressed a novel, single domain lectin from Macrolepiota procera, designated MpL. Determination of the crystal structure revealed that MpL is a ricin B-like lectin with a β-trefoil fold. Biochemical characterization, site-directed mutagenesis, co-crystallization with carbohydrates, isothermal titration calorimetry and glycan microarray analyses show that MpL forms dimers with the carbohydrate-binding site at the α-repeat, with the highest specificity for terminal N-acetyllactosamine and other β-galactosides. A second putative carbohydrate-binding site with a low affinity for galactose is present at the γ-repeat. In addition, a novel hydrophobic binding site was detected in MpL with specificity for molecules other than carbohydrates. The tissue specific distribution of MpL in the stipe and cap tissue of fruiting bodies and its toxicity towards the nematode Caenorhabditis elegans indicate a function of MpL in protecting fruiting bodies against predators and parasites.
  
  
  METHODS
  Nucleotide sequence data have been deposited in the DDBJ/EMBL/GenBank databases under accession numbers HQ449738 and HQ449739. Structural data have been deposited in the Protein Data Bank under accession codes 4ION, 4IYB, 4IZX and 4J2S.
authors.affiliation: Department of Biotechnology, Jožef Stefan Institute, Ljubljana, Slovenia.
authors.forename: Simon
authors.initials: S
authors.lastname: Žurga
authors.forename: Jure
authors.initials: J
authors.lastname: Pohleven
authors.forename: Miha
authors.initials: M
authors.lastname: Renko
authors.forename: Silvia
authors.initials: S
authors.lastname: Bleuler-Martinez
authors.forename: Piotr
authors.initials: P
authors.lastname: Sosnowski
authors.forename: Dušan
authors.initials: D
authors.lastname: Turk
authors.forename: Markus
authors.initials: M
authors.lastname: Künzler
authors.forename: Janko
authors.initials: J
authors.lastname: Kos
authors.forename: Jerica
authors.initials: J
authors.lastname: Sabotič
mesh_terms: D000363:Agaricales / Q000378:metabolism*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D000969:Antinematodal Agents / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D001665:Binding Sites; D017173:Caenorhabditis elegans / Q000187:drug effects; D002240:Carbohydrate Sequence; D018360:Crystallography, X-Ray; D048690:Fruiting Bodies, Fungal / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D006860:Hydrogen Bonding; D037102:Lectins / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011134:Polysaccharides / Q000737:chemistry; D011485:Protein Binding; D017433:Protein Structure, Secondary
chemical_list: D000969:Antinematodal Agents; D005656:Fungal Proteins; D037102:Lectins; D011134:Polysaccharides
keywords: LacNAc; basidiomycete; galactose; lectin; ricin B-like