The trimeric solution structure and fucose-binding mechanism of the core fucosylation-specific lectin PhoSL

Kazuhiko Yamasaki, Tomoko Yamasaki, Hiroaki Tateno
2018 Scientific Reports  
The core α1-6 fucosylation-specific lectin from a mushroom Pholiota squarrosa (PhoSL) is a potential tool for precise diagnosis of cancers. This lectin consists of only 40 amino acids and can be chemically synthesized. We showed here that a synthesized PhoSL peptide formed a trimer by gel filtration and chemical cross-linking assays, and determined a structure of the PhoSL trimer by NMR. The structure possesses a β-prism motif with a three-fold rotational symmetry, where three antiparallel
more » ... ets are tightly connected by swapping of β-strands. A triad of Trp residues comprises the structural core, forming NH-π electrostatic interactions among the indole rings. NMR analysis with an excess amount of fucose revealed the structural basis for the molecular recognition. Namely, fucose deeply enters a pocket formed at a junction of β-sheet edges, with the methyl group placed at the bottom. It forms a number of hydrophobic and hydrogen-bonding interactions with PhoSL residues. In spite of partial similarities to the structures of other functionally related lectins, the arrangement of the antiparallel β-sheets in the PhoSL trimer is novel as a structural scaffold, and thus defines a novel type of lectin structure. Fucosylation is a common modification in glycoproteins, and is classified into several types with regard to the modes of linkage, i.e., α1-2, α1-3, α1-4, and α1-6. Among them, the α1-6 fucosylation is typically found at the first N-acetyl-D-glucosamine (GlcNAc) of the N-glycan core (called "core" fucosylation) in the mammalian systems, and is keenly related to cancer development 1 . Most prominently, the level of core fucosylation of N-glycan in alpha-fetoprotein (AFP) increases in hepatocellular carcinomas (HCC) and carcinoma metastatic to the liver, but not in benign liver diseases, such as acute viral hepatitis, chronic hepatitis, or liver cirrhosis 2 . This was explained by selective secretion of fucosylated glycoproteins produced in hepatocyte through bile duct, although such bile duct does not exist in tissues of the carcinomas 1 . Therefore, lectins specific to core fucosylation should be particularly useful for the diagnostics of these cancers. A lectin highly specific to core α1-6 fucosylation was recently isolated from a mushroom Pholiota squarrosa (PhoSL) 3 . PhoSL binds only to core-fucosylated glycans, but not to the other types of fucosylated glycans, as revealed by frontal affinity chromatography 4 . In addition, this lectin showed stronger affinity than that of a clinically used lectin Lens culinaris agglutinin (LCA). Therefore, researchers started to use PhoSL for detecting core fucosylation in diagnosis of cancers and related diseases, i.e., colorectal, prostate, pancreatic, and liver cancers as well as a chronic pancreatitis that is a background of pancreatic ductal adenocarcinoma 5-9 . The PhoSL molecule purified from the mushroom consists of only 40 residues and can therefore be chemically synthesized 3 . It is likely that PhoSL exists in a trimeric or tetrameric form, as shown by gel filtration, mass spectrometry, and gel electrophoresis analyses 3 . This lectin showed an extreme stability against heat treatment, e.g., 100 °C for 30 min, and also against incubation at pH 2-11. PhoSL is therefore suitable for its use as a medical tool in that it is easy to produce and to keep in the active form. Moreover, it would be easier to incorporate unnatural amino acids by means of the chemical synthesis, in order to produce lectins with novel specificities. Published: xx xx xxxx OPEN www.nature.com/scientificreports/ 2 ScIeNTIfIc REPORTS | (2018) 8:7740 |
doi:10.1038/s41598-018-25630-2 pmid:29773815 pmcid:PMC5958098 fatcat:wjgbjyybn5b4fodml4u4hg4kc4