Structural model of phospholipid-reconstituted human transferrin receptor derived by electron microscopy
Structural model of phospholipid-reconstituted human transferrin receptor derived by electron microscopy
复制标题
DOI：
10.1016/s0969-2126(98)00124-5
复制
发表时间：
1998-10-01
期刊：
影响因子：
5.7
通讯作者：
Gessner, R
中科院分区：
文献类型：
--
作者：
Fuchs, H;Lücken, U;Gessner, R
背景：转铁蛋白受体（TfR）调节细胞对血清铁的摄取。尽管 TfR 作为内吞受体的模型系统，但晶体结构分析和电子显微镜尚未揭示 TfR 的分子尺寸。为了导出第一个分子模型，我们通过高分辨率电子显微镜分析了纯化的脂质重组人 TfR。结果：从 72 张冷冻电子显微镜图像中得出磷脂重组 TfR 的结构模型。 TfR 二聚体由一个大的细胞外球状结构域 (6.4 x 7.5 x 10.5 nm) 组成，通过细分子茎 (2.9 nm) 与膜分开。比较蛋白质序列分析表明，茎对应于氨基酸残基 89-126。在磷脂重建条件下，人类 TfR 不仅整合到囊泡中，而且形成称为蛋白质颗粒的玫瑰花状结构。扫描透射电子显微镜显示蛋白质颗粒的总直径为 31.5 nm，分子量为 1669 +/- 26 kDa，对应于九个 TfR 二聚体。单个受体二聚体的平均质量确定为 186 +/- 4 kDa。结论：蛋白质颗粒类似于成熟时由绵羊网织红细胞排出的 TfR 外泌体。因此，体外蛋白质颗粒的结构被解释为 TfR 强大的自缔合潜力的结果，这可能促进 TfR 与其他膜蛋白的内体隔离，并随后返回管状结构内的细胞表面。推测茎有利于受体分子在包被的凹坑和回收小管中紧密堆积。
Background: The transferrin receptor (TfR) regulates the cellular uptake of serum iron. Although the TfR serves as a model system for endocytosis receptors, neither crystal structure analysis nor electron microscopy has yet revealed the molecular dimensions of the TfR. To derive the first molecular model, we analyzed purified, lipid-reconstituted human TfR by high-resolution electron microscopy.Results: A structural model of phospholipid-reconstituted TfR was derived from 72 cryo-electron microscopic images. The TfR dimer consists of a large extracellular globular domain (6.4 x 7.5 x 10.5 nm) separated from the membrane by a thin molecular stalk (2.9 nm). A comparative protein sequence analysis suggests that the stalk corresponds to amino acid residues 89-126. Under phospholipid-reconstitution conditions, the human TfR not only integrates into vesicles, but also forms rosette-like structures called proteoparticles. Scanning transmission electron microscopy revealed an overall diameter of 31.5 nm and a molecular mass of 1669 +/- 26 kDa for the proteoparticles, corresponding to nine TfR dimers. The average mass of a single receptor dimer was determined as being 186 +/- 4 kDa.Conclusions: Proteoparticles resemble TfR exosomes that are expelled by sheep reticulocytes upon maturation. The structure of proteoparticles in vitro is thus interpreted as being the result of the TfR's strong self-association potential, which might facilitate the endosomal sequestration of the TfR away from other membrane proteins and its subsequent return to the cell surface within tubular structures. The stalk is assumed to facilitate the tight packing of receptor molecules in coated pits and recycling tubuli.