Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), U964/Centre National de Recherche Scientifique (CNRS) UMR 7104/Université de Strasbourg, Illkirch, France.
PLoS One. 2011 Mar 31;6(3):e18124. doi: 10.1371/journal.pone.0018124.
The 1α,25-dihydroxy-3-epi-vitamin-D3 (1α,25(OH)2-3-epi-D3), a natural metabolite of the seco-steroid vitamin D3, exerts its biological activity through binding to its cognate vitamin D nuclear receptor (VDR), a ligand dependent transcription regulator. In vivo action of 1α,25(OH)2-3-epi-D3 is tissue-specific and exhibits lowest calcemic effect compared to that induced by 1α,25(OH)2D3. To further unveil the structural mechanism and structure-activity relationships of 1α,25(OH)2-3-epi-D3 and its receptor complex, we characterized some of its in vitro biological properties and solved its crystal structure complexed with human VDR ligand-binding domain (LBD).
METHODOLOGY/PRINCIPAL FINDINGS: In the present study, we report the more effective synthesis with fewer steps that provides higher yield of the 3-epimer of the 1α,25(OH)2D3. We solved the crystal structure of its complex with the human VDR-LBD and found that this natural metabolite displays specific adaptation of the ligand-binding pocket, as the 3-epimer maintains the number of hydrogen bonds by an alternative water-mediated interaction to compensate the abolished interaction with Ser278. In addition, the biological activity of the 1α,25(OH)2-3-epi-D3 in primary human keratinocytes and biochemical properties are comparable to 1α,25(OH)2D3.
CONCLUSIONS/SIGNIFICANCE: The physiological role of this pathway as the specific biological action of the 3-epimer remains unclear. However, its high metabolic stability together with its significant biologic activity makes this natural metabolite an interesting ligand for clinical applications. Our new findings contribute to a better understanding at molecular level how natural metabolites of 1α,25(OH)2D3 lead to significant activity in biological systems and we conclude that the C3-epimerization pathway produces an active metabolite with similar biochemical and biological properties to those of the 1α,25(OH)2D3.
1α,25-二羟-3-表维生素 D3（1α,25(OH)2-3-epi-D3）是维生素 D3 的天然代谢物，通过与其同源维生素 D 核受体（VDR）结合发挥其生物活性，VDR 是一种配体依赖性转录调节剂。1α,25(OH)2-3-epi-D3 的体内作用具有组织特异性，与 1α,25(OH)2D3 诱导的作用相比，其钙调节作用最低。为了进一步揭示 1α,25(OH)2-3-epi-D3 及其受体复合物的结构机制和构效关系，我们对其一些体外生物学特性进行了表征，并解析了其与人类 VDR 配体结合域（LBD）复合物的晶体结构。
方法/主要发现：在本研究中，我们报告了更有效的合成方法，该方法步骤更少，产率更高，可获得更多的 1α,25(OH)2D3 的 3-差向异构体。我们解析了其与人类 VDR-LBD 复合物的晶体结构，发现这种天然代谢物显示出配体结合口袋的特异性适应，因为 3-差向异构体通过替代的水介导相互作用保持氢键的数量，以补偿与 Ser278 丧失的相互作用。此外，1α,25(OH)2-3-epi-D3 在原代人角质形成细胞中的生物学活性和生化特性与 1α,25(OH)2D3 相当。
结论/意义：该途径的生理作用作为 3-差向异构体的特定生物学作用尚不清楚。然而，其较高的代谢稳定性及其显著的生物活性使这种天然代谢物成为一种有趣的临床应用配体。我们的新发现有助于更好地理解分子水平上 1α,25(OH)2D3 的天然代谢物如何导致生物系统中显著的活性，我们得出结论，C3-差向异构化途径产生具有与 1α,25(OH)2D3 相似生化和生物学特性的活性代谢物。
