Abstract: Human cystatin C (HCC), a cysteine-protease inhibitor, exists as a folded monomer under physiological conditions but has the ability to self-assemble via domain swapping into multimeric states, including oligomers with a doughnut-like structure. The structure of the monomeric HCC has been solved by X-ray crystallography, and a covalently linked version of HCC (stab-1 HCC) is able to form stable oligomeric species containing 10-12 monomeric subunits. We have performed molecular modeling, and in conjunction with experimental parameters obtained from AFM, TEM and SAXS measurements, we observe that the structures are essentially flat, with a height of about 2 nm, and the distance between the outer edge of the ring and the edge of the central cavity is ~5.1 nm. These dimensions correspond to the height and diameter of one stab-1 HCC subunit and we present a dodecamer model for stabilized cystatin C oligomers using molecular dynamics simulations and experimentally measured parameters. Given that oligomeric species in protein aggregation reactions are often transient and very highly heterogeneous, the structural information presented here on these isolated stab-1 HCC oligomers may provide useful to further explore the physiological relevance of different structural species of cystatin C in relationship to protein misfolding disease

中文翻译：

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共价稳定的人胱抑素C寡聚体的结构表征

摘要：人胱抑素C（HCC）是一种半胱氨酸蛋白酶抑制剂，在生理条件下以折叠单体形式存在，但具有通过结构域交换成多聚体状态（包括具有甜甜圈状结构的低聚物）而自组装的能力。单体HCC的结构已通过X射线晶体学解决，并且HCC的共价连接形式（stab-1 HCC）能够形成包含10-12个单体亚基的稳定寡聚体。我们已经进行了分子建模，并结合了从AFM，TEM和SAXS测量获得的实验参数，我们观察到结构基本上是平坦的，高度约为2 nm，并且环的外边缘和表面之间的距离中央腔的边缘约为5.1 nm。这些尺寸对应于一个stab-1 HCC亚基的高度和直径，我们使用分子动力学模拟和实验测量的参数，给出了稳定的半胱氨酸蛋白酶抑制剂C低聚物的dodecamer模型。鉴于蛋白质聚集反应中的寡聚物种通常是短暂的且非常不均一，因此本文介绍的这些分离的stab-1 HCC寡聚体的结构信息可能为进一步探索胱抑素C不同结构物种与蛋白质错折叠的生理相关性提供有用的信息疾病