Department of Chemistry, Division of Advanced Material Science, BK School of Molecular Science, Pohang University of Science and Technology, Pohang, Republic of Korea.
Biomacromolecules. 2011 May 9;12(5):1629-40. doi: 10.1021/bm200026v. Epub 2011 Apr 8.
The pH-dependent structures of the ferritin shell (apoferritin, 24-mer) and the ferrihydrite core, under physiological conditions that permit enzymatic activity, were investigated by synchrotron small-angle X-ray scattering (SAXS). The solution structure of apoferritin was found to be nearly identical to the crystal structure. The shell thickness and hollow core volumes were estimated. The intact hollow spherical apoferritin was stable over a wide pH range, 3.40-10.0, and the ferrihydrite core was stable over the pH range 2.10-10.0. The apoferritin subunits underwent aggregation below pH 0.80, whereas the ferrihydrite cores aggregated below pH 2.10 as a result of the disassembly of the ferritin shell under the strongly acidic conditions. As the pH decreased from 3.40 to 0.80, apoferritin underwent stepwise disassembly by first forming a hollow sphere with two holes, then a headset-shaped structure, and, finally, rodlike oligomers. As the pH was increased from pH 1.96, the disassembled rodlike oligomers recovered only to the headset-shaped structure, and the disassembled headset-shaped intermediates recovered only to the hollow spherical structure with two hole defects. The apoferritin hole defects that formed during the disassembly process did not heal as the pH was increased to neutral or slightly basic conditions. The pH-induced apoferritin disassembly and reassembly processes were not fully reversible, although they were pseudoreversible over a limited pH range, between 10.0 and 2.66.
在允许酶活性的生理条件下，通过同步加速器小角 X 射线散射（SAXS）研究了铁蛋白壳（脱铁铁蛋白，24 聚体）和水铁矿核的 pH 依赖性结构。发现脱铁铁蛋白的溶液结构与晶体结构几乎相同。估算了壳厚度和中空核体积。完整的中空球形脱铁铁蛋白在很宽的 pH 范围内（3.40-10.0）稳定，而水铁矿核在 pH 范围内（2.10-10.0）稳定。脱铁铁蛋白亚基在 pH 低于 0.80 时发生聚集，而水铁矿核在 pH 低于 2.10 时发生聚集，这是由于在强酸性条件下铁蛋白壳的解体导致的。当 pH 值从 3.40 降低到 0.80 时，脱铁铁蛋白通过首先形成具有两个孔的中空球体，然后形成耳机形结构，最后形成棒状低聚物，逐步解体。当 pH 值从 1.96 增加时，解组装的棒状低聚物仅恢复到耳机形结构，并且解组装的耳机形中间体仅恢复到具有两个孔缺陷的中空球形结构。在组装过程中形成的脱铁铁蛋白孔缺陷不会随着 pH 值增加到中性或略碱性条件而愈合。尽管在有限的 pH 范围内（10.0 和 2.66 之间）是假可逆的，但 pH 诱导的脱铁铁蛋白解组装和组装过程不是完全可逆的。
