Structural insights for vanadium catecholates and iron sulfur clusters obtained from multiple data analysis methods applied to electron spin relaxation data
Structural insights for vanadium catecholates and iron sulfur clusters obtained from multiple data analysis methods applied to electron spin relaxation data
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DOI：
10.1016/j.jinorgbio.2019.110806
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发表时间：
2019-12-01
影响因子：
3.9
通讯作者：
Eaton, Sandra S.
中科院分区：
文献类型：
--
作者：
Ngendahimana, Thacien;Ayikpoe, Richard;Eaton, Sandra S.
采用两个指数和、一个拉伸指数和一个无模型指数分布（UPEN）三种模型分析了儿茶酚酸钒和铁硫簇的电子顺磁共振（EPR）反演恢复曲线。对于所研究的所有数据集，拉伸指数的拟合在统计上与两个指数的和难以区分，并且明显优于单个指数。UPEN提供了对发行版结构的深入了解。对于钒（IV）三儿茶酚酸盐，用UPEN计算的弛豫速率分布显示了低温下光谱扩散的贡献。从自旋晶格弛豫的温度依赖性中发现，该配合物的局部模式能量与金属配体振动的预期值一致。对于丙酮酸甲酸裂解酶激活酶（PFL-AE）中的[2Fe-2S]（+）簇，在低温下的小拉伸指数β值（0.3）和UPEN计算的分布反映了第二种快速松弛的物质的贡献，这种物质很难通过连续波EPR检测到。分枝杆菌素成熟酶[4Fe-4S]（+）簇在1/T-1中的分布比其他3个系统宽约4倍。弛豫率的广泛分布可能是由于蛋白质的迁移率和电子能量的分布以及簇的局部环境。UPEN提供了几种可能导致拉伸参数β值较低的情况的见解，包括光谱扩散的贡献，来自可区分簇的重叠信号，或非常宽的分布。
Electron paramagnetic resonance (EPR) inversion recovery curves for vanadium catecholates and iron-sulfur clusters were analyzed with three models: the sum of two exponentials, a stretched exponential, and a model-free distribution of exponentials (UPEN). For all data sets studied fits with a stretched exponential were statistically indistinguishable from the sum of two exponentials, and were significantly better than for single exponentials. UPEN provides insights into the structures of the distributions. For a vanadium(IV) tris catecholate the distribution of relaxation rates calculated with UPEN shows the contribution from spectral diffusion at low temperatures. The energy of the local mode for this complex, found from the temperature dependence of the spin lattice relaxation, is consistent with values expected for a metal-ligand vibration. For the [2Fe-2S](+) cluster in pyruvate formate lyase activating enzyme (PFL-AE) the small stretched exponential beta values (0.3) at low temperature and the distributions calculated with UPEN reflect the contribution from a second rapidly relaxing species that could be difficult to detect by continuous wave EPR. The distributions in 1/T-1 for the [4Fe-4S](+) clusters in Mycofactocin maturase were about a factor of four wider than for the three other systems studied. The very broad distribution of relaxation rates may be due to protein mobility and distributions in electronic energies and local environments for the clusters. UPEN provides insight into several situations that can result in low values of stretch parameter beta including contributions from spectral diffusion, overlapping signals from distinguishable clusters, or very wide distributions.