High potential iron–sulfur proteins (HiPIPs) are a class of small proteins (50–100 aa residues), containing a 4Fe–4S iron–sulfur cluster. The 4Fe–4S cluster shuttles between the oxidation states [Fe₄S₄]^3+/2+, with a positive redox potential in the range (500–50 mV) throughout the different known HiPIPs. Both oxidation states are paramagnetic at room temperature. HiPIPs are electron transfer proteins, isolated from photosynthetic bacteria and usually provide electrons to the photosynthetic reaction-center. PioC, the HIPIP isolated from Rhodopseudomonas palustris TIE-1, is the smallest among all known HiPIPs. Despite their small dimensions, an extensive NMR assignment is only available for two of them, because paramagnetism prevents the straightforward assignment of all resonances. We report here the complete NMR assignment of ¹H, ¹³C and ¹⁵N signals for the reduced [Fe₄S₄]²⁺ state of the protein. A set of double and triple resonance experiments performed with standardized parameters/datasets provided the assignment of about 72% of the residues. The almost complete resonance assignment (99.5% of backbone and ca. 90% of side chain resonances) was achieved by combining the above information with those obtained using a second set of NMR experiments, in which acquisition and processing parameters, as well as pulse sequences design, were optimized to account for the peculiar features of this paramagnetic protein.

中文翻译：

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来自沼泽红假单胞菌 TIE-1 的顺磁性高电位铁硫蛋白 (HiPIP) PioC 的 1H、13C 和 15N 分配。

高电位铁硫蛋白 (HiPIP) 是一类小蛋白（50-100 个氨基酸残基），含有 4Fe-4S 铁硫簇。4Fe–4S 簇在氧化态 [Fe ₄ S ₄ ] ^3+/2+之间穿梭，在不同的已知 HiPIP 中具有范围 (500–50 mV) 的正氧化还原电位。两种氧化态在室温下都是顺磁性的。HiPIP 是电子转移蛋白，从光合细菌中分离出来，通常为光合反应中心提供电子。PioC，从沼泽红假单胞菌TIE-1 中分离的 HIPIP ，是所有已知 HiPIP 中最小的。尽管它们的尺寸很小，但只有其中两个可以使用广泛的 NMR 分配，因为顺磁性阻止了所有共振的直接分配。我们在此报告了还原的 [Fe ₄ S ₄ ] ²⁺的¹ H、¹³ C 和¹⁵ N 信号的完整 NMR 分配蛋白质的状态。使用标准化参数/数据集进行的一组双和三重共振实验提供了约 72% 的残基分配。几乎完全的共振分配（主链的 99.5% 和侧链共振的约 90%）是通过将上述信息与使用第二组 NMR 实验获得的信息相结合来实现的，其中采集和处理参数，以及脉冲序列设计，被优化以解释这种顺磁性蛋白质的特殊特征。