title: Crystal structure of a Xenopus laevis skin proto-type galectin, close to but distinct from galectin-1.
abstract: Xenopus laevis (African clawed frog) has two types of proto-type galectins that are similar to mammalian galectin-1 in amino acid sequence. One type, comprising xgalectin-Ia and -Ib, is regarded as being equivalent to galectin-1, and the other type, comprising xgalectin-Va and -Vb, is expected to be a unique galectin subgroup. The latter is considerably abundant in frog skin; however, its biological function remains unclear. We determined the crystal structures of two proto-type galectins, xgalectin-Ib and -Va. The structures showed that both galectins formed a mammalian galectin-1-like homodimer, and furthermore, xgalectin-Va formed a homotetramer. This tetramer structure has not been reported for other galectins. Gel filtration and other experiments indicated that xgalectin-Va was in a dimer-tetramer equilibrium in solution, and lactose binding enhanced the tetramer formation. The residues involved in the dimer-dimer association were conserved in xgalectin-Va and -Vb, and one of the Xenopus (Silurana) tropicalis proto-type galectins, but not in xgalectin-Ia and -Ib, and other galectin-1-equivalent proteins. Xgalectin-Va preferred Galβ1-3GalNAc and not Galβ1-4GlcNAc, while xgalectin-Ib preferred Galβ1-4GlcNAc as well as human galectin-1. Xgalectin-Va/Vb would have diverged from the galectin-1 group with accompanying acquisition of the higher oligomer formation and altered ligand selectivity.
authors: Department of Endocrinology, Faculty of Medicine.
authors: Yasuhiro
authors: Y
authors: Nonaka
authors: Department of Endocrinology, Faculty of Medicine.
authors: Takashi
authors: T
authors: Ogawa
authors: Life Science Research Center, Kagawa University, Kagawa, Japan.
authors: Hiromi
authors: H
authors: Yoshida
authors: Department of Endocrinology, Faculty of Medicine Department of Biology, Kanazawa Medical University, Ishikawa, Japan.
authors: Hiroki
authors: H
authors: Shoji
authors: Life Science Research Center, Kagawa University, Kagawa, Japan.
authors: Nozomu
authors: N
authors: Nishi
authors: Life Science Research Center, Kagawa University, Kagawa, Japan.
authors: Shigehiro
authors: S
authors: Kamitori
authors: Department of Endocrinology, Faculty of Medicine tnaka@med.kagawa-u.ac.jp.
authors: Takanori
authors: T
authors: Nakamura
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002236:Carbohydrate Conformation; D018360:Crystallography, X-Ray; D037161:Galectins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D012867:Skin / Q000378:metabolism*; D014982:Xenopus laevis / Q000378:metabolism*
chemical_list: D037161:Galectins
keywords: X-ray crystallography; Xenopus laevis; amphibian skin secretion; galectin