title: C-type lectin-like carbohydrate recognition of the hemolytic lectin CEL-III containing ricin-type -trefoil folds.
abstract: CEL-III is a Ca(2+)-dependent hemolytic lectin, isolated from the marine invertebrate Cucumaria echinata. The three-dimensional structure of CEL-III/GalNAc and CEL-III/methyl alpha-galactoside complexes was solved by x-ray crystallographic analysis. In these complexes, five carbohydrate molecules were found to be bound to two carbohydrate-binding domains (domains 1 and 2) located in the N-terminal 2/3 portion of the polypeptide and that contained beta-trefoil folds similar to ricin B-chain. The 3-OH and 4-OH of bound carbohydrate molecules were coordinated with Ca(2+) located at the subdomains 1alpha, 1gamma, 2alpha, 2beta, and 2gamma, simultaneously forming hydrogen bond networks with nearby amino acid side chains, which is similar to carbohydrate binding in C-type lectins. The binding of carbohydrates was further stabilized by aromatic amino acid residues, such as tyrosine and tryptophan, through a stacking interaction with the hydrophobic face of carbohydrates. The importance of amino acid residues in the carbohydrate-binding sites was confirmed by the mutational analyses. The orientation of bound GalNAc and methyl alpha-galactoside was similar to the galactose moiety of lactose bound to the carbohydrate-binding site of the ricin B-chain, although the ricin B-chain does not require Ca(2+) ions for carbohydrate binding. The binding of the carbohydrates induced local structural changes in carbohydrate-binding sites in subdomains 2alpha and 2beta. Binding of GalNAc also induced a slight change in the main chain structure of domain 3, which could be related to the conformational change upon binding of specific carbohydrates to induce oligomerization of the protein.
authors.affiliation: Department of Applied Chemistry, Faculty of Engineering, Nagasaki University, Nagasaki, Japan. thata@nagasaki-u.ac.jp
authors.forename: Tomomitsu
authors.initials: T
authors.lastname: Hatakeyama
authors.forename: Hideaki
authors.initials: H
authors.lastname: Unno
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Kouzuma
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Uchida
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Eto
authors.forename: Haruki
authors.initials: H
authors.lastname: Hidemura
authors.forename: Norihisa
authors.initials: N
authors.lastname: Kato
authors.forename: Masami
authors.initials: M
authors.lastname: Yonekura
authors.forename: Masami
authors.initials: M
authors.lastname: Kusunoki
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002241:Carbohydrates / Q000737:chemistry*; D002462:Cell Membrane / Q000378:metabolism; D018360:Crystallography, X-Ray / Q000379:methods; D048016:Cucumaria / Q000378:metabolism*; D007477:Ions; D037102:Lectins / Q000737:chemistry*; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D011485:Protein Binding; D017510:Protein Folding; D012276:Ricin / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid
chemical_list: D002241:Carbohydrates; D007477:Ions; D037102:Lectins; C059525:cerebellar soluble lectin; D012276:Ricin