title: Sugar-complex structures of the C-half domain of the galactose-binding lectin EW29 from the earthworm Lumbricus terrestris.
abstract: R-type lectins are one of the most prominent types of lectin; they exist ubiquitously in nature and mainly bind to the galactose unit of sugar chains. The galactose-binding lectin EW29 from the earthworm Lumbricus terrestris belongs to the R-type lectin family as represented by the plant lectin ricin. It shows haemagglutination activity and is composed of a single peptide chain that includes two homologous domains: N-terminal and C-terminal domains. A truncated mutant of EW29 comprising the C-terminal domain (rC-half) has haemagglutination activity by itself. In order to clarify how rC-half recognizes ligands and shows haemagglutination activity, X-ray crystal structures of rC-half in complex with D-lactose and N-acetyl-D-galactosamine have been determined. The structure of rC-half is similar to that of the ricin B chain and consists of a beta-trefoil fold; the fold is further divided into three similar subdomains referred to as subdomains alpha, beta and gamma, which are gathered around the pseudo-threefold axis. The structures of sugar complexes demonstrated that subdomains alpha and gamma of rC-half bind terminal galactosyl and N-acetylgalactosaminyl glycans. The sugar-binding properties are common to both ligands in both subdomains and are quite similar to those of ricin B chain-lactose complexes. These results indicate that the C-terminal domain of EW29 uses these two galactose-binding sites for its function as a single-domain-type haemagglutinin.
authors.affiliation: Protein Research Unit, National Institute of Agrobiological Sciences, Tsukuba 305-8602, Japan.
authors.forename: Ryuichiro
authors.initials: R
authors.lastname: Suzuki
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kuno
authors.forename: Tsunemi
authors.initials: T
authors.lastname: Hasegawa
authors.forename: Jun
authors.initials: J
authors.lastname: Hirabayashi
authors.forename: Ken Ichi
authors.initials: KI
authors.lastname: Kasai
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Momma
authors.forename: Zui
authors.initials: Z
authors.lastname: Fujimoto
mesh_terms: D000116:Acetylgalactosamine / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002241:Carbohydrates / Q000737:chemistry; D018360:Crystallography, X-Ray; D005690:Galactose / Q000378:metabolism; D037161:Galectins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007785:Lactose / Q000378:metabolism; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000378:metabolism; D050505:Mutant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D009835:Oligochaeta; D011485:Protein Binding; D011487:Protein Conformation; D012276:Ricin / Q000737:chemistry* / Q000378:metabolism; D017384:Sequence Deletion; D013329:Structure-Activity Relationship
chemical_list: D002241:Carbohydrates; C542531:EW29 lectin, Lumbricus terrestris; D037161:Galectins; D046912:Multiprotein Complexes; D050505:Mutant Proteins; D012276:Ricin; D007785:Lactose; D000116:Acetylgalactosamine; D005690:Galactose