C-type lectin-like carbohydrate recognition of the hemolytic lectin CEL-III containing ricin-type -trefoil folds.
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.
Hatakeyama
Tomomitsu
T
Department of Applied Chemistry, Faculty of Engineering, Nagasaki University, Nagasaki, Japan. thata@nagasaki-u.ac.jp
Unno
Hideaki
H
Kouzuma
Yoshiaki
Y
Uchida
Tatsuya
T
Eto
Seiichiro
S
Hidemura
Haruki
H
Kato
Norihisa
N
Yonekura
Masami
M
Kusunoki
Masami
M
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
D002241:Carbohydrates; D007477:Ions; D037102:Lectins; C059525:cerebellar soluble lectin; D012276:Ricin