Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 789 South Limestone Street, Lexington, KY, 40536-0596, USA.
Xiangya School of Pharmaceutical Sciences, Central South University, Changsha, Hunan, 410013, P. R. China.
Angew Chem Int Ed Engl. 2020 Jan 7;59(2):826-832. doi: 10.1002/anie.201910241. Epub 2019 Nov 27.
MtmOIV and MtmW catalyze the final two reactions in the mithramycin (MTM) biosynthetic pathway, the Baeyer-Villiger opening of the fourth ring of premithramycin B (PMB), creating the C3 pentyl side chain, strictly followed by reduction of the distal keto group on the new side chain. Unexpectedly this results in a C2 stereoisomer of mithramycin, iso-mithramycin (iso-MTM). Iso-MTM undergoes a non-enzymatic isomerization to MTM catalyzed by Mg ions. Crystal structures of MtmW and its complexes with co-substrate NADPH and PEG, suggest a catalytic mechanism of MtmW. The structures also show that a tetrameric assembly of this enzyme strikingly resembles the ring-shaped β subunit of a vertebrate ion channel. We show that MtmW and MtmOIV form a complex in the presence of PMB and NADPH, presumably to hand over the unstable MtmOIV product to MtmW, yielding iso-MTM, as a potential self-resistance mechanism against MTM toxicity.
MtmOIV 和 MtmW 催化了密曲霉素 (MTM) 生物合成途径中的最后两个反应，即前密曲霉素 B (PMB) 的第四个环的 Baeyer-Villiger 开环反应，生成 C3 戊基侧链，严格遵循新侧链上远端酮基的还原。出乎意料的是，这导致了密曲霉素的 C2 立体异构体，异密曲霉素 (iso-MTM)。异密曲霉素在镁离子的催化下发生非酶促异构化，转化为密曲霉素。MtmW 及其与共底物 NADPH 和 PEG 复合物的晶体结构表明了 MtmW 的催化机制。这些结构还表明，这种酶的四聚体组装非常类似于脊椎动物离子通道的环形 β 亚基。我们表明，MtmW 和 MtmOIV 在 PMB 和 NADPH 的存在下形成复合物，可能是将不稳定的 MtmOIV 产物递交给 MtmW，生成异密曲霉素，作为一种潜在的自我抵抗机制，以抵御 MTM 的毒性。
