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首页> 外文期刊>Biochemistry >Crystal Structures of Parasponia and Trema Hemoglobins: Differential Heme Coordination Is Linked to Quaternary Structure
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Crystal Structures of Parasponia and Trema Hemoglobins: Differential Heme Coordination Is Linked to Quaternary Structure

机译：副孢子菌和Trema血红蛋白的晶体结构：血红素微分配位链接到第四级结构。

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摘要

Hemoglobins from the plants Parasponia andersonii (ParaHb) and Trema tomentosa (TremaHb) are 93% identical in primary structure but differ in oxygen binding constants in accordance with their distinct physiological functions. Additionally, these proteins are dimeric, and ParaHb exhibits the unusual property of having different heme redox potentials for each subunit. To investigate how these hemoglobins could differ in function despite their shared sequence identity and to determine the cause of subunit heterogeneity in ParaHb, we have measured their crystal structures in the ferric oxidation state. Furthermore, we have made a monomeric ParaHb mutant protein (I43N) and measured its ferrous/ferric heme redox potential to test the hypothesized link between quaternary structure and heme heterogeneity in wild-type ParaHb. Our results demonstrate that TremaHb is a symmetric dimeric hemoglobin similar to other class 1 nonsymbiotic plant hemoglobins but that ParaHb has structurally distinct heme coordination in each of its two subunits that is absent in the monomeric I43N mutant protein. A mechanism for achieving structural heterogeneity in ParaHb in which the Ile~(101(F4)) side chain contacts the proximal His~(105(F8)) in one subunit but not the other is proposed. These results are discussed in the context of the evolution of plant oxygen transport hemoglobins, and other potential functions of plant hemoglobins.
机译：来自植物Parasponia andersonii（ParaHb）和Trema tomentosa（TremaHb）的血红蛋白在一级结构上具有93％的同一性，但根据其独特的生理功能，其氧结合常数不同。此外，这些蛋白质是二聚体，并且ParaHb表现出不同寻常的特性，即每个亚基具有不同的血红素氧化还原电位。为了研究这些血红蛋白尽管具有相同的序列同一性，在功能上如何可能不同，并确定ParaHb中亚基异质性的原因，我们测量了它们在三氧化二铁状态下的晶体结构。此外，我们制备了单体ParaHb突变蛋白（I43N），并测量了其亚铁/铁血红素氧化还原电位，以测试野生型ParaHb中四级结构与血红素异质性之间的假想联系。我们的结果表明，TremaHb是一种对称的二聚体血红蛋白，与其他1类非共生植物血红蛋白相似，但ParaHb在其两个亚基中均存在结构上独特的血红素配体，而单体I43N突变蛋白中却没有。提出了一种在ParaHb中实现结构异质性的机制，其中Ile_（101（F4））侧链在一个亚基中与近端His_（105（F8））在一个亚基中接触。在植物氧转运血红蛋白的进化以及植物血红蛋白的其他潜在功能的背景下讨论了这些结果。

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