Dipartimento di Scienze della Vita e dell'Ambiente, Università Politecnica delle Marche, Via Ranieri, 60131 Ancona, Italy.
Biochimie. 2013 Feb;95(2):158-66. doi: 10.1016/j.biochi.2012.09.005. Epub 2012 Sep 17.
Human α(1)-acid glycoprotein (AGP) is a positive acute phase plasma protein containing two disulfide bridges. Structural studies have shown that under specific conditions AGP undergoes aggregation. In this study, we analysed the nature of AGP's aggregates formed under reducing and non-reducing conditions at pH 5.5 and at relatively low temperatures. Thioflavin T and Congo red spectroscopic analyses indicated the presence of cross-β structures in both unreduced and reduced AGP aggregates. In these samples amyloid-like fibrils were detected by transmission electron microscopy. The fibrils are branched and bent and present in very large amount in reduced AGP. Kinetics of AGP fibrillation proceeds without a lag phase and the rate constants of cross-β formation are linearly dependent on AGP concentration and result higher under reducing conditions. The data suggest a possible downhill mechanism of polymerization with a first-order monomer concentration dependence. Bioinformatics tools highlighted an extended region that sheathes one side of the molecule containing aggregation-prone regions. Reducing conditions make the extended region less constricted, allowing greater exposure of aggregation-prone regions, thus explaining the higher propensity of AGP to aggregate and fibrillate.
人α(1)-酸性糖蛋白 (AGP) 是一种正急性相血浆蛋白，含有两个二硫键。结构研究表明，在特定条件下，AGP 会发生聚集。在这项研究中，我们分析了在 pH 值为 5.5 和相对较低温度下，还原和非还原条件下形成的 AGP 聚集体的性质。硫黄素 T 和刚果红光谱分析表明，在未还原和还原的 AGP 聚集体中都存在交叉-β结构。在这些样品中，通过透射电子显微镜检测到了类似淀粉样纤维。这些纤维呈分支状和弯曲状，在还原型 AGP 中大量存在。AGP 纤维化的动力学没有滞后期，交叉-β形成的速率常数与 AGP 浓度呈线性相关，并且在还原条件下更高。数据表明聚合可能存在下坡机制，单体浓度呈一级依赖性。生物信息学工具突出了一个扩展区域，该区域包裹分子的一侧，其中包含易于聚集的区域。还原条件使扩展区域的束缚程度降低，从而使易于聚集的区域更大程度地暴露，从而解释了 AGP 更容易聚集和纤维化的原因。
