School of Engineering & Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK.
Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow, G4 0RE Scotland, UK.
Cell Signal. 2020 Dec;76:109806. doi: 10.1016/j.cellsig.2020.109806. Epub 2020 Oct 7.
The sphingosine kinases, SK1 and SK2, catalyse the formation of the bioactive signalling lipid, sphingosine 1-phosphate (S1P), from sphingosine. SK1 and SK2 differ in their subcellular localisation, trafficking and regulation, but the isoforms are also distinct in their selectivity toward naturally occurring and synthetic ligands as substrates and inhibitors. To date, only the structure of SK1 has been determined, and a structural basis for selectivity differences in substrate handling by SK2 has yet to be established. Here we present a structural rationale, based on homology modelling and ligand docking, to account for the capacity of SK2, but not SK1, to efficiently process the pharmacologically active substances, fingolimod (FTY720) and safingol, as substrates. We propose that two key residue differences in hSK2 (Ser305/Thr584 in place of Ala175/Ala339 in hSK1) facilitate conformational switching in the lipid head group anchor residue, Asp308 (corresponding to Asp178 in hSK1), to accommodate substrate diversity for SK2. Our analysis accounts for the contrasting behaviour of fingolimod and safingol as non-turnover inhibitors of SK1, but substrates for SK2, and the observed stereoselectivity for phosphorylation of the pro-S hydroxymethyl group of fingolimod to generate (S)-FTY720-P in vivo. We also rationalise why methylation of the pro-R hydroxymethyl of FTY720 switches the behaviour of the resulting compound, (R)-FTY720 methyl ether (ROMe), to SK2-selective inhibition. Whilst the pharmacological significance of (S)-FTY720-P is firmly established, as the active principle of fingolimod in treating relapsing-remitting multiple sclerosis, the potential importance of SK-mediated phosphorylation of other substrates, such as safingol and non-canonical naturally occuring substrates such as (4E,nZ)-sphingadienes, is less widely appreciated. Thus, the contribution of SK2-derived safingol 1-phosphate to the anti-cancer activity of safingol should be considered. Similarly, the biological role of sphingadiene 1-phosphates derived from plant-based dietary sphingadienes, which we also show here are substrates for both SK1 and SK2, merits investigation.
鞘氨醇激酶 1（SK1）和 2（SK2）催化鞘氨醇转化为生物活性信号脂质 1-磷酸鞘氨醇（S1P）。SK1 和 SK2 的亚细胞定位、运输和调节不同，但同工酶在天然和合成配体作为底物和抑制剂的选择性方面也存在差异。迄今为止，仅确定了 SK1 的结构，并且尚未建立 SK2 对底物处理的选择性差异的结构基础。在这里，我们基于同源建模和配体对接提出了一个结构原理，以解释 SK2 而不是 SK1 有效处理药理学上活跃的物质， fingolimod（FTY720）和 safingol 的能力。我们提出 hSK2 中的两个关键残基差异（Ser305/Thr584 取代 hSK1 中的 Ala175/Ala339）促进了脂质头部锚定残基 Asp308 的构象转换（对应于 hSK1 中的 Asp178），以适应 SK2 的底物多样性。我们的分析解释了 fingolimod 和 safingol 作为 SK1 的非周转率抑制剂但 SK2 的底物的相反行为，以及在体内生成（S）-FTY720-P 时对 fingolimod 的 pro-S 羟甲基的磷酸化的观察到的立体选择性。我们还解释了为什么 FTY720 的 pro-R 羟甲基的甲基化会使生成的化合物（R）-FTY720 甲基醚（ROMe）的行为转变为 SK2 选择性抑制。虽然（S）-FTY720-P 的药理学意义已得到牢固确立，作为 fingolimod 在治疗复发缓解型多发性硬化症中的活性成分，但 SK 介导的其他底物（如 safingol 和非典型天然存在的底物如（4E，nZ）-鞘氨二烯）的磷酸化的潜在重要性尚未得到广泛认识。因此，应该考虑 SK2 衍生的 safingol 1-磷酸对 safingol 的抗癌活性的贡献。同样，我们还在这里展示了植物源性鞘氨二烯的生物活性，我们也表明它们是 SK1 和 SK2 的底物，值得进一步研究。
