Shen Jiemin, Wu Gang, Pierce Brad S, Tsai Ah-Lim, Zhou Ming
Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
Department of Internal Medicine, University of Texas McGovern Medical School, Houston, TX 77030, USA.
bioRxiv. 2023 Mar 18:2023.03.17.533000. doi: 10.1101/2023.03.17.533000.
Mammalian stearoyl-CoA desaturase-1 (SCD1) introduces a double-bond to a saturated long-chain fatty acid and the reaction is catalyzed by a diiron center, which is well-coordinated by conserved histidine residues and is thought to remain with enzyme. However, we find that SCD1 progressively loses its activity during catalysis and becomes fully inactive after nine turnovers. Further studies show that the inactivation of SCD1 is due to the loss of an iron (Fe) ion in the diiron center, and that the addition of free ferrous ions (Fe ) sustains the enzymatic activity. Using SCD1 labeled with Fe isotope, we further show that free Fe is incorporated into the diiron center only during catalysis. We also discover that the diiron center in SCD1 has prominent electron paramagnetic resonance signals in its diferric state, indicative of distinct coupling between the two ferric ions. These results reveal that the diiron center in SCD1 is structurally dynamic during catalysis and that labile Fe in cells could regulate SCD1 activity, and hence lipid metabolism.
哺乳动物硬脂酰辅酶A去饱和酶-1（SCD1）将一个双键引入饱和长链脂肪酸中，该反应由一个双铁中心催化，该双铁中心由保守的组氨酸残基良好配位，并且被认为与酶结合在一起。然而，我们发现SCD1在催化过程中逐渐失去活性，在九次周转后完全失活。进一步的研究表明，SCD1的失活是由于双铁中心中铁（Fe）离子的丢失，并且添加游离亚铁离子（Fe²⁺）可维持酶活性。使用用Fe同位素标记的SCD1，我们进一步表明游离Fe²⁺仅在催化过程中掺入双铁中心。我们还发现SCD1中的双铁中心在其二价铁状态下具有明显的电子顺磁共振信号，表明两个铁离子之间存在独特的耦合。这些结果表明，SCD1中的双铁中心在催化过程中结构动态变化，细胞中不稳定的Fe²⁺可以调节SCD1活性，从而调节脂质代谢。
