Implication of molecular diversity and functional conservation of erythropoietin based on a comparison of tertiary structures of humans and frogs

ツメガエルエリスロポエチンの性状解析と分子構造の進化的保存性

目黒 瑞枝; 安達 基泰; 永澤 和道*; 別府 実穂*; 岡崎 伸生; 小坂 菜美*; 玉田 太郎; 黒木 良太; 加藤 尚志

Meguro, Mizue; Adachi, Motoyasu; Nagasawa, Kazumichi*; Beppu, Miho*; Okazaki, Nobuo; Kosaka, Nami*; Tamada, Taro; Kuroki, Ryota; Kato, Takashi

The tertiary structure of cytokine-receptor complex provides information about molecular interactions trigger the receptor activation, the primary event of physiological response. To further our understanding of structural basis of cytokines, cross-species comparison of a cytokine structure is an important clue. When we identified erythropoietin (EPO) in African clawed frog, Xenopus laevis, namely xlEPO, it was our surprise that xlEPO shares only 38% of the amino acid sequence with human EPO (hEPO) and lacks N-glycosylation. Dispite the low molecular similarity, xlEPO could stimulate proliferation and differentiation of erythrocytic cells transcending species. These findings lead us to explore a particular topology specific to EPO-EPOR binding by solving the crystal structure of xlEPO that enables us to compare the tertiary structures of EPO. In this study, we determined the crystal structure of unbound form of xlEPO. xlEPO exhibited extremely similar topology to hEPO, and the -carbon root mean square distance between xlEPO and hEPO are 2.35 and 3.06 , with 1EER and the NMR structure (1BUY), respectively. The tertiary structure of receptor-binding form of xlEPO would enable us to understand the conformational change of xlEPO, and to design EPO mimetics based on newer concepts.