The a-cluster in subunit β of the acetyl-CoA decarbonylase/synthase complex from Methanosarcina thermophila:: Ni and FeK-Edge XANES and EXAFS analyses
The a-cluster in subunit β of the acetyl-CoA decarbonylase/synthase complex from Methanosarcina thermophila:: Ni and FeK-Edge XANES and EXAFS analyses
复制标题
DOI：
10.1021/ja036602a
复制
发表时间：
2003-12-17
影响因子：
15
通讯作者：
Grahame, DA
中科院分区：
文献类型：
--
作者：
Gu, WW;Gencic, S;Grahame, DA
乙酰辅酶a脱碳酶/合成酶（ACDS）复合物在甲烷菌中催化乙酰辅酶a的裂解，将乙酸代谢为CO2和CH4，并在单碳底物生长过程中进行乙酰辅酶a的合成。ACDS配合物包含5个亚基，其中β具有一个Ni-Fe-S活性位点的金属簇，即a簇，在a簇上与乙酰辅酶a发生反应，生成一个乙酰酶，准备裂解C-C键。我们使用Ni和Fe K荧光XANES和EXAFS分析来表征ACDS β亚基中的这些金属，这些金属以c端缩短形式表达。Fe XANES和EXAFS证实了[Fe4S4]簇的存在，典型的Fe- s和Fe-Fe距离分别为2.3和2.7埃。通过Kalphabeta荧光分析发现Fe:Ni的比值近似于2:1，表明2 Ni / [Fe4S4]。Ni XANES模拟结果与A簇中两个不同的Ni位点一致，并且观测到的光谱可以被建模为单独的方形平面和四面体Ni位点的总和。用Ti3+柠檬酸盐处理β亚基导致能量向较低的方向转移，这意味着[Fe4S4]中心的显著减少，同时Ni（II）转化为Ni(I)的比例更小。在Ti3+柠檬酸盐存在下与CO反应产生了独特的Ni XANES光谱，而对fe边缘的影响与单独与Ti3+反应没有太大区别。Ni EXAFS在2.19埃时平均配位为2.5 S，在1.89埃时平均配位为1.5 N/O。类似于2.95埃的明显特征很可能是Ni-Ni相互作用的结果。甲烷菌β亚基a -簇由一个桥接在Ni-Ni中心的[Fe4S4]簇组成，其中一个Ni为2 S + 2 N配位的方形平面几何，另一个为3 S + 1 N/O配位的近似四面体。讨论了两种不同Ni几何形状的电子结果。
The acetyl-CoA decarbonylase/synthase (ACDS) complex catalyzes the cleavage of acetyl-CoA in methanogens that metabolize acetate to CO2 and CH4, and also carries out acetyl-CoA synthesis during growth on one-carbon substrates. The ACDS complex contains five subunits, among which beta possesses an Ni-Fe-S active-site metal cluster, the A-cluster, at which reaction with acetyl-CoA takes place, generating an acetyl-enzyme species poised for C-C bond cleavage. We have used Ni and Fe K fluorescence XANES and EXAFS analyses to characterize these metals in the ACDS beta subunit, expressed as a C-terminally shortened form. Fe XANES and EXAFS confirmed the presence of an [Fe4S4] cluster, with typical Fe-S and Fe-Fe distances of 2.3 and 2.7 Angstrom respectively. An Fe:Ni ratio of similar to2:1 was found by Kalphabeta fluorescence analysis, indicating 2 Ni per [Fe4S4]. Ni XANES simulations were consistent with two distinct Ni sites in cluster A, and the observed spectrum could be modeled as the sum of separate square planar and tetrahedral Ni sites. Treatment of the beta subunit with Ti3+ citrate resulted in shifts to lower energy, implying significant reduction of the [Fe4S4] center, along with conversion of a smaller fraction of Ni(II) to Ni(I). Reaction with CO in the presence of Ti3+ citrate generated a unique Ni XANES spectrum, while effects on the Fe-edge were not very different from the reaction with Ti3+ alone. Ni EXAFS revealed an average Ni coordination of 2.5 S at 2.19 Angstrom and 1.5 N/O at 1.89 Angstrom. A distinct feature at similar to2.95 Angstrom most likely results from Ni-Ni interaction. The methanogen beta subunit A-cluster is proposed to consist of an [Fe4S4] cluster bridged to an Ni-Ni center with one Ni in square planar geometry coordinated by 2 S + 2 N and the other approximately tetrahedral with 3 S + 1 N/O ligands. The electronic consequences of two distinct Ni geometries are discussed.