Crystallographic and Spectroscopic Insights into Heme Degradation by Mycobacterium tuberculosis MhuD

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• 作者：Amanda B. Graves ; Robert P. Morse ; Alex Chao ; Angelina Iniguez ; Celia W. Goulding ; Matthew D. Liptak
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：June 16, 2014
• 年：2014
• 卷：53
• 期：12
• 页码：5931-5940
• 全文大小：489K
• 年卷期：v.53,no.12(June 16, 2014)
• ISSN：1520-510X

文摘

Mycobacterium heme utilization degrader (MhuD) is a heme-degrading protein from Mycobacterium tuberculosis responsible for extracting the essential nutrient iron from host-derived heme. MhuD has been previously shown to produce unique organic products compared to those of canonical heme oxygenases (HOs) as well as those of the IsdG/I heme-degrading enzymes from Staphylococcus aureus. Here, we report the X-ray crystal structure of cyanide-inhibited MhuD (MhuD鈥揾eme鈥揅N) as well as detailed ¹H nuclear magnetic resonance (NMR), UV/vis absorption, and magnetic circular dichroism (MCD) spectroscopic characterization of this species. There is no evidence for an ordered network of water molecules on the distal side of the heme substrate in the X-ray crystal structure, as was previously reported for canonical HOs. The degree of heme ruffling in the crystal structure of MhuD is greater than that observed for HO and less than that observed for IsdI. As a consequence, the Fe 3d_xz-, 3d_yz-, and 3d_xy-based MOs are very close in energy, and the room-temperature ¹H NMR spectrum of MhuD鈥揾eme鈥揅N is consistent with population of both a ²E_g electronic state with a (d_xy)²(d_xz,d_yz)³ electron configuration, similar to the ground state of canonical HOs, and a ²B_2g state with a (d_xz,d_yz)⁴(d_xy)¹ electron configuration, similar to the ground state of cyanide-inhibited IsdI. Variable temperature, variable field MCD saturation magnetization data establishes that MhuD鈥揾eme鈥揅N has a ²B_2g electronic ground state with a low-lying ²E_g excited state. Our crystallographic and spectroscopic data suggest that there are both structural and electronic contributions to the 伪-meso regioselectivity of MhuD-catalyzed heme cleavage. The structural distortion of the heme substrate observed in the X-ray crystal structure of MhuD鈥揾eme鈥揅N is likely to favor cleavage at the 伪- and 纬-meso carbons, whereas the spin density distribution may favor selective oxygenation of the 伪-meso carbon.