Extended X-ray absorption fine structure and nuclear resonance vibrational Spectroscopy reveal that NifB-co, a FeMo-co precursor, comprises a 6Fe core with an interstitial light atom
Extended X-ray absorption fine structure and nuclear resonance vibrational Spectroscopy reveal that NifB-co, a FeMo-co precursor, comprises a 6Fe core with an interstitial light atom
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DOI：
10.1021/ja0755358
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发表时间：
2008-04-30
影响因子：
15
通讯作者：
Cramer, Stephen P.
中科院分区：
文献类型：
--
作者：
George, Simon J.;Igarashi, Robert Y.;Cramer, Stephen P.
NifB-co是由NifB酶产生的Fe-S簇，是固氮酶铁钼辅因子（FeMo-co）生物合成途径的中间体。我们使用Fe K边扩展X射线吸收精细结构（EXAFS）光谱与57 Fe核共振振动光谱（NRVS）一起探测NifB-co的结构，同时结合到棕色固氮菌的NifX蛋白。光谱已被解释部分通过与完整的FeMo-co连接到NafY载体蛋白的数据：NafY：FeMo-co复合物的比较。NifX：NifB-co复合物的EXAFS分析得到平均Fe-S距离为2.26埃，平均Fe-Fe距离为2.66和3.74埃。搜索配置文件分析揭示了一个单一的Fe-X（X = C，N，或O）在2.04埃的相互作用的存在下，相比，在NafY：FeMo-co EXAFS中发现的2.00埃的Fe-X相互作用。这表明提出存在于FeMo-co中的间隙轻原子（X）已经在生物合成的NifB-co阶段插入。NRVS表现出来自Fe-S伸缩模的强带，峰值在270、315、385和408 cm（-1）附近。类似于185-200 cm（-1）的额外强度被解释为一组簇“呼吸”模式，类似于FeMo辅因子所见的模式。这些模式的强度和位置也表明，在晶体结构中看到的FeMo-co间隙轻原子已经在NifB-co中就位。NifX：NifB-co的EXAFS和NRVS数据最好使用类似于FeMo-co的6 Fe核心的Fe 6S 9 X三角棱柱结构来模拟，尽管不能排除通过用Fe覆盖一个三角3S末端而制成的7 Fe结构。结果是一致的结论，即间隙轻原子已经存在于早期阶段，在铁钼-co-生物合成之前，纳入钼和R-高柠檬酸。
NifB-co, an Fe-S cluster produced by the enzyme NifB, is an intermediate on the biosynthetic pathway to the iron molybdenum cofactor (FeMo-co) of nitrogenase. We have used Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy together with 57 Fe nuclear resonance vibrational spectroscopy (NRVS) to probe the structure of NifB-co while bound to the NifX protein from Azotobacter vinelandii. The spectra have been interpreted in part by comparison with data for the completed FeMo-co attached to the NafY carrier protein: the NafY:FeMo-co complex. EXAFS analysis of the NifX:NifB-co complex yields an average Fe-S distance of 2.26 angstrom and average Fe-Fe distances of 2.66 and 3.74 angstrom. Search profile analyses reveal the presence of a single Fe-X (X = C, N, or O) interaction at 2.04 angstrom, compared to a 2.00 angstrom Fe-X interaction found in the NafY:FeMo-co EXAFS. This suggests that the interstitial light atom (X) proposed to be present in FeMo-co has already inserted at the NifB-co stage of biosynthesis. The NRVS exhibits strong bands from Fe-S stretching modes peaking around 270, 315, 385, and 408 cm(-1). Additional intensity at similar to 185-200 cm(-1) is interpreted as a set of cluster "breathing" modes similar to those seen for the FeMo-cofactor. The strength and location of these modes also suggest that the FeMo-co interstitial light atom seen in the crystal structure is already in place in NifB-co. Both the EXAFS and NRVS data for NifX:NifB-co are best simulated using a Fe6S9X trigonal prism structure analogous to the 6Fe core of FeMo-co, although a 7Fe structure made by capping one trigonal 3S terminus with Fe cannot be ruled out. The results are consistent with the conclusion that the interstitial light atom is already present at an early stage in FeMo-co-biosynthesis prior to the incorporation of Mo and R-homocitrate.