Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011, USA.
Department of Chemistry, University of Wisconsin-Parkside, Kenosha, WI 53141, USA.
Molecules. 2018 Oct 6;23(10):2546. doi: 10.3390/molecules23102546.
Isoprenyl chains are found in many important metabolites. These are derived from precursors of the appropriate length produced by isoprenyl diphosphate synthases (IDSs). The human pathogen makes various isoprenoids/terpenoids, with important roles in their biosynthesis played by two closely related IDSs, encoded by (Rv0562) and (Rv0989c), with Rv0989c generating the 10-carbon precursor ()-geranyl diphosphate (GPP), and Rv0562 the 20-carbon precursor ()-geranylgeranyl diphosphate (GGPP). Intriguingly, while Rv0562 contains the prototypical -IDS first and second aspartate-rich (DDxxD) motifs (FARM and SARM, respectively), Rv0989c uniquely contains arginine in place of the second Asp in the FARM and first Asp in the SARM. Here site-directed mutagenesis of the corresponding residues in both Rv0562 and Rv0989c reveals that these play a role in determination of product chain length. Specifically, substitution of Asp for the Arg in the FARM and SARM of Rv0989c leads to increased production of the longer 15-carbon farnesyl diphosphate (FPP), while substitution of Arg for the corresponding Asp in Rv0562 leads to increased release of shorter products, both FPP and GPP. Accordingly, while the primary role of the FARM and SARM is known to be chelation of the divalent magnesium ion co-factors that assist substrate binding and catalysis, the Arg substitutions found in Rv0989c seem to provide a novel means by which product chain length is moderated, at least in these IDSs.
异戊烯基链存在于许多重要的代谢物中。这些代谢物源自异戊烯二磷酸合酶（IDS）产生的适当长度的前体。人类病原体产生各种异戊烯/萜烯，其生物合成中由两个密切相关的 IDS 起重要作用，由 （Rv0562）和 （Rv0989c）编码，Rv0989c 生成 10 碳前体 ()-香叶基二磷酸（GPP），而 Rv0562 生成 20 碳前体 ()-法呢基二磷酸（GGPP）。有趣的是，虽然 Rv0562 包含典型的 -IDS 第一个和第二个富天冬氨酸（DDxxD）基序（FARM 和 SARM），但 Rv0989c 独特地在 FARM 的第二个 Asp 和 SARM 的第一个 Asp 处用精氨酸取代。这里对 Rv0562 和 Rv0989c 中的相应残基进行定点突变表明，这些残基在确定产物链长中起作用。具体而言，FARM 和 SARM 中的 Asp 取代 Rv0989c 中的 Arg 会导致更长的 15 碳法尼基二磷酸（FPP）产量增加，而 Rv0562 中 Arg 取代相应的 Asp 会导致更短产物（FPP 和 GPP）的释放增加。因此，虽然已知 FARM 和 SARM 的主要作用是螯合二价镁离子辅助因子，该因子协助底物结合和催化，但在 Rv0989c 中发现的 Arg 取代似乎提供了一种调节产物链长的新方法，至少在这些 IDS 中是这样。
