A multinuclear ENDOR study of the C-cluster in CO dehydrogenase from Clostridium thermoaceticum:: Evidence for HxO and histidine coordination to the [Fe4S4] center
A multinuclear ENDOR study of the C-cluster in CO dehydrogenase from Clostridium thermoaceticum:: Evidence for HxO and histidine coordination to the [Fe4S4] center
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DOI：
10.1021/ja9731480
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发表时间：
1998-09-02
影响因子：
15
通讯作者：
Hoffman, BM
中科院分区：
文献类型：
--
作者：
DeRose, VJ;Telser, J;Hoffman, BM
一氧化碳脱氢酶（CODH）的C簇催化CO的可逆氧化以形成CO2。本研究报告的电子核双共振（ENDOR）光谱的单电子还原（C-red1），CN-抑制，和CO（或连二亚硫酸盐）-还原（C-red2）形式的C-簇从热醋酸梭菌CODH（CODHCt）。所观察到的H-1，H-2，N-14，C-13和Fe-57的超精细相互作用支持并扩展了当前的Ni-X-[Fe4S4] C簇模型，其中[Fe4S4]中心通过独特的铁FCII与Ni离子连接。未成对电子自旋显然是本地化的[Fe4S4]组件的集群，因此ENDOR观察到的超精细相互作用最有可能反映与该组件相关的物种。一个溶剂可交换的质子与A（H-1）= 16 MHz的最大超精细耦合被检测到的C-red 1的形式，但不是在CN-抑制或C-red 2的形式。可交换的质子被分配到一个可能的溶剂衍生的（HxO，x = 1，2）配体FCII的C-red 1 [Fe 4S 4]（1+）中心，并预测是一个基板在CO/CO2催化。对于C-red 1和C-red 2，我们发现ENDOR功能的预期区域的氮供体配体，这可能是从组氨酸配体的[Fe 4 S 4]中心。Fe-57 ENDOR检测到C-red 1中至少两类Fe，它们最有可能来自（Fe2.5+）（2）混合价对。它们的A（Fe-57）> 40 MHz的最大耦合支持了簇的不寻常性质;这些在酶的C-red 1和C-red 2形式之间没有显着变化。通过用（CO）-C-13还原形成的C-red 2没有显示新的C-13特征，强烈地表明CO及其氧化产物都不与C-red 2中的[Fe 4S 4]中心结合。总之，这些ENDOR分配表明在C-red 1状态下，CODH C-簇的独特Fe离子具有稳定结合HxO或CN-的可用配位位点，簇合导致在该位点的重排，导致结合的水性配体的损失。
The C-cluster of carbon monoxide dehydrogenase (CODH) catalyzes the reversible oxidation of CO to form CO2. This study reports electron nuclear double resonance (ENDOR) spectroscopy of the one-electron reduced (C-red1), the CN--inhibited, and the CO (or dithionite)-reduced (C-red2) forms of the C-cluster from Clostridium thermoaceticum CODH (CODHCt). The observed hyperfine interactions of H-1,H-2,N-14, C-13, and Fe-57 support and extend the current Ni-X-[Fe4S4] C-cluster model in which a [Fe4S4] center is linked to a Ni ion through a unique iron, FCII. The unpaired electron spin apparently is localized on the [Fe4S4] component of the cluster, and thus the hyperfine interactions observed by ENDOR most probably reflect species associated with that component. A solvent-exchangeable proton with a maximum hyperfine coupling of A(H-1) = 16 MHz is detected in the C-red1 form, but not in the CN--inhibited or C-red2 forms. The exchangeable proton is assigned to a probable solvent-derived (HxO, x = 1, 2) ligand to FCII of the C-red1 [Fe4S4](1+) center and is predicted to be a substrate in CO/CO2 catalysis. For both C-red1 and C-red2, We find ENDOR features in the region expected for a nitrogen-donor ligand which likely arise from a histidine ligand to the [Fe4S4] center. Fe-57 ENDOR detects at least two classes of Fe in C-red1 that most likely arise from the (Fe2.5+)(2) mixed-valence pair. Their large maximum couplings of A(Fe-57) > 40 MHz support the unusual nature of the cluster; these do not change dramatically between the C-red1 and C-red2 forms of the enzyme. C-red2 formed by reduction with (CO)-C-13 reveals no new C-13 features, strongly suggesting that neither CO nor its oxidized products are bound to the [Fe4S4] center in C-red2 Taken together, these ENDOR assignments suggest that in the C-red1 state, the unique Fe ion of the CODH C-cluster has an available coordination site that stably binds HxO or CN- and that reduction of the C-cluster results in rearrangement at that site, causing loss of the bound aqueous ligand.