High-resolution structure of the conger eel galectin, congerin I, in lactose-liganded and ligand-free forms: Emergence of a new structure class by accelerated evolution

Tsuyoshi Shirai, Clara Mitsuyama, Yuusuke Niwa, Yuuka Matsui, Hiroshi Hotta, Takashi Yamane, Hisao Kamiya, Chihiro Ishii, Tomohisa Ogawa, Koji Muramoto

研究成果: Article

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Background: Congerin I is a member of the galectin (animal β- galactoside-binding lectin) family and is found in the skin mucus of conger eel. The galectin family proteins perform a variety of biological activities. Because of its histological localization and activity against marine bacteria and starfish embryos, congerin I is thought to take part in the eels' biological defense system against parasites. Results: The crystal structure of congerin I has been determined in both lactose-liganded and ligand-free forms to 1.5 Å and 1.6 Å resolution, respectively. The protein is a homodimer of 15 kDa subunits. Congerin I has a β-sheet topology that is markedly different from those of known relatives. One of the β-strands is exchanged between two identical subunits. This strand swap might increase the dimer stability. Of the known galectin complexes, congerin I forms the most extensive interaction with lactose molecules. Most of these interactions are substituted by similar interactions with water molecules, including a π- electron hydrogen bond, in the ligand-free form. This observation indicates an increased affinity of congerin I for the ligand. Conclusions: The genes for congerin I and an isoform, congerin II, are known to have evolved under positive selection pressure. The strand swap and the modification in the carbohydrate-binding site might enhance the cross-linking activity, and should be the most apparent consequence of positive selection. The protein has been adapted to functioning in skin mucus that is in direct contact with surrounding environments by an enhancement in cross-linking activity. The structure of congerin I demonstrates the emergence of a new structure class by accelerated evolution under selection pressure.

元の言語English
ページ(範囲)1223-1233
ページ数11
ジャーナルStructure
7
発行部数10
DOI
出版物ステータスPublished - 1999 10 15

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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