BACKGROUND S100 proteins are a large family of calcium binding proteins present only in vertebrates. They function intra- and extracellularly both as regulators of homeostatic processes and as potent effectors during inflammation. Among these, S100A8 and S100A9 are two major constituents of neutrophils that can assemble into homodimers, heterodimers and higher oligomeric species, including fibrillary structures found in the ageing prostate. Each of these forms assumes specific functions and their formation is dependent on divalent cations, notably calcium and zinc. In particular, zinc appears as a major regulator of S100 protein function in a disease context. Despite this central role, no structural information on how zinc bind to S100A8/S100A9 and regulates their quaternary structure is yet available. RESULTS Here we report two crystallographic structures of calcium and zinc-loaded human S100A8. S100A8 binds two zinc ions per homodimer, through two symmetrical, all-His tetracoordination sites, revealing a classical His-Zn binding mode for the protein. Furthermore, the presence of a (Zn)2-cacodylate complex in our second crystal form induces ligand swapping within the canonical His4 zinc binding motif, thereby creating two new Zn-sites, one of which involves residues from symmetry-related molecules. Finally, we describe the calcium-induced S100A8 tetramer and reveal how zinc stabilizes this tetramer by tightening the dimer-dimer interface. CONCLUSIONS Our structures of Zn(2+)/Ca(2+)-bound hS100A8 demonstrate that S100A8 is a genuine His-Zn S100 protein. Furthermore, they show how zinc stabilizes S100A8 tetramerization and potentially mediates the formation of novel interdimer interactions. We propose that these zinc-mediated interactions may serve as a basis for the generation of larger oligomers in vivo.

中文翻译：

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人S100A8与锌和钙复合的晶体结构。

背景技术S100蛋白是仅存在于脊椎动物中的钙结合蛋白的大家族。它们在细胞内和细胞外均起着体内稳态过程的调节剂的作用，并在炎症过程中起着强效的作用。其中，S100A8和S100A9是嗜中性粒细胞的两个主要成分，可以组装成同型二聚体，异二聚体和高级寡聚体，包括在老化的前列腺中发现的原纤维结构。这些形式中的每一种都具有特定的功能，并且它们的形成取决于二价阳离子，尤其是钙和锌。特别是在疾病中，锌似乎是S100蛋白功能的主要调节剂。尽管起着中心作用，但尚无关于锌如何与S100A8 / S100A9结合并调节其四级结构的结构信息。结果在这里我们报告钙和锌载人S100A8的两个晶体结构。S100A8通过两个对称的全His四配位位点结合每个同二聚体两个锌离子，从而揭示了该蛋白的经典His-Zn结合方式。此外，在我们的第二种晶型中存在（Zn）2-甲藻酸酯复合物会诱导规范的His4锌结合基序内的配体交换，从而产生两个新的Zn位点，其中一个涉及对称相关分子的残基。最后，我们描述了钙诱导的S100A8四聚体，并揭示了锌如何通过加强二聚体-二聚体界面来稳定该四聚体。结论我们的Zn（2 +）/ Ca（2+）结合hS100A8的结构表明S100A8是真正的His-Zn S100蛋白。此外，它们显示了锌如何稳定S100A8四聚体并潜在地介导新的二聚体相互作用的形成。我们建议这些锌介导的相互作用可以作为体内较大寡聚物的产生的基础。