Department of Chemistry-Ångström Laboratory, Uppsala University, Uppsala, Sweden.
Department of Chemistry, Umeå University, Umeå, Sweden.
PLoS One. 2019 Aug 1;14(8):e0218300. doi: 10.1371/journal.pone.0218300. eCollection 2019.
Dps proteins (DNA-binding proteins from starved cells) have been found to detoxify H2O2. At their catalytic centers, the ferroxidase center (FOC), Dps proteins utilize Fe2+ to reduce H2O2 and therefore play an essential role in the protection against oxidative stress and maintaining iron homeostasis. Whereas most bacteria accommodate one or two Dps, there are five different Dps proteins in Nostoc punctiforme, a phototrophic and filamentous cyanobacterium. This uncommonly high number of Dps proteins implies a sophisticated machinery for maintaining complex iron homeostasis and for protection against oxidative stress. Functional analyses and structural information on cyanobacterial Dps proteins are rare, but essential for understanding the function of each of the NpDps proteins. In this study, we present the crystal structure of NpDps4 in its metal-free, iron- and zinc-bound forms. The FOC coordinates either two iron atoms or one zinc atom. Spectroscopic analyses revealed that NpDps4 could oxidize Fe2+ utilizing O2, but no evidence for its use of the oxidant H2O2 could be found. We identified Zn2+ to be an effective inhibitor of the O2-mediated Fe2+ oxidation in NpDps4. NpDps4 exhibits a FOC that is very different from canonical Dps, but structurally similar to the atypical one from DpsA of Thermosynechococcus elongatus. Sequence comparisons among Dps protein homologs to NpDps4 within the cyanobacterial phylum led us to classify a novel FOC class: the His-type FOC. The features of this special FOC have not been identified in Dps proteins from other bacterial phyla and it might be unique to cyanobacterial Dps proteins.
Dps 蛋白（饥饿细胞中的 DNA 结合蛋白）已被发现能够解毒 H2O2。在其催化中心，亚铁氧化酶中心（FOC），Dps 蛋白利用 Fe2+ 还原 H2O2，因此在抵御氧化应激和维持铁平衡方面发挥着重要作用。虽然大多数细菌仅容纳一个或两个 Dps，但在蓝藻 Nostoc punctiforme 中存在五种不同的 Dps 蛋白。这种异常高数量的 Dps 蛋白意味着存在一种复杂的机制来维持复杂的铁平衡和抵御氧化应激。对蓝藻 Dps 蛋白的功能分析和结构信息很少，但对于理解每种 NpDps 蛋白的功能至关重要。在这项研究中，我们展示了 NpDps4 在其无金属、铁和锌结合形式下的晶体结构。FOC 配位两个铁原子或一个锌原子。光谱分析表明，NpDps4 可以利用 O2 氧化 Fe2+，但没有发现其使用氧化剂 H2O2 的证据。我们发现 Zn2+ 是 NpDps4 中 O2 介导的 Fe2+氧化的有效抑制剂。NpDps4 表现出的 FOC 与典型的 Dps 非常不同，但在结构上与来自 Thermosynechococcus elongatus 的 DpsA 的非典型 FOC 相似。在蓝藻门内与 NpDps4 同源的 Dps 蛋白同源物之间的序列比较使我们将一种新型 FOC 分类：His 型 FOC。这种特殊 FOC 的特征尚未在其他细菌门的 Dps 蛋白中被识别，它可能是蓝藻 Dps 蛋白所独有的。
