Sugimoto H, Taniguchi M, Nakagawa A, Tanaka I, Suzuki M, Nishihira J
Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan.
Biochemistry. 1999 Mar 16;38(11):3268-79. doi: 10.1021/bi982184o.
D-Dopachrome tautomerase shares a low homologous amino acid sequence (33% homology) with the macrophage migration inhibitory factor (MIF) and possesses similar tautomerase activity as well. MIF is a cytokine involved in inflammatory reactions and immune responses. Whereas recent studies have identified MIF as a pituitary hormone and immunoregulator, much less is known about the structural basis of these physiological functions and the real significance of tautomerase activity. Therefore, interest in the structure-function relationship between D-dopachrome tautomerase and MIF has increased, especially with regard to inflammation and immune responses. We have determined the X-ray crystal structure of human D-dopachrome tautomerase at 1.54 A resolution. D-Dopachrome tautomerase folds to form a homotrimer that has extensive contact between subunits by intersubunit beta-sheets. Its overall topology and trimeric formations are similar to those of human MIF. The N-terminal proline is located at the bottom of a positively charged pocket in which the conformations of Lys32 and Ser63 are highly conserved. These positively charged properties are also seen in the active site pocket of human MIF, bacterial 5-(carboxymethyl)-2-hydroxymuconate isomerase (CHMI), and 4-oxalocrotonate tautomerase (4-OT). A detailed comparison of these structures revealed significant differences in the environment around the potential active site, the intersubunit contacts, and charge distribution on the molecular surface. It can be concluded that these features are related to the physiological role and tautomerase activity of MIF and D-dopachrome tautomerase. The present structural study could be helpful for designing effective inhibitors that modulate immunoregulatory and hormone-like effects.
D - 多巴色素互变异构酶与巨噬细胞迁移抑制因子（MIF）的氨基酸序列同源性较低（33%同源性），并且也具有类似的互变异构酶活性。MIF是一种参与炎症反应和免疫应答的细胞因子。尽管最近的研究已将MIF鉴定为一种垂体激素和免疫调节因子，但对于这些生理功能的结构基础以及互变异构酶活性的实际意义却知之甚少。因此，人们对D - 多巴色素互变异构酶与MIF之间的结构 - 功能关系的兴趣增加了，特别是在炎症和免疫应答方面。我们已经确定了人D - 多巴色素互变异构酶的X射线晶体结构，分辨率为1.54埃。D - 多巴色素互变异构酶折叠形成同源三聚体，亚基之间通过亚基间β - 折叠片层有广泛的接触。其整体拓扑结构和三聚体形式与人类MIF相似。N末端脯氨酸位于带正电荷口袋的底部，其中Lys32和Ser63的构象高度保守。在人类MIF、细菌5 - （羧甲基） - 2 - 羟基粘康酸异构酶（CHMI）和4 - 草酰巴豆酸互变异构酶（4 - OT）的活性位点口袋中也可见到这些带正电荷的特性。对这些结构的详细比较揭示了潜在活性位点周围环境、亚基间接触以及分子表面电荷分布的显著差异。可以得出结论，这些特征与MIF和D - 多巴色素互变异构酶的生理作用及互变异构酶活性有关。目前的结构研究可能有助于设计出能调节免疫调节和激素样作用的有效抑制剂。
